From d096395958fc61bbe8184ee9b67d35b432042ca9 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Fri, 25 Aug 2023 10:20:28 -0400
Subject: [PATCH] Move tests to separate directories, and document

Today, with the tests inside a `tests` intermingled with the
corresponding library's source code, we have a few problems:

- We have to be careful that wildcards don't end up with tests being
  built as part of Nix proper, or test headers being installed as part
  of Nix proper.

- Understanding `#include` resolution is very hard, because files
  instead `tests` directories can shadow those outside by mistake.

This solves the first problem and partially solves the second problem
--- test headers still need to live inside a `tests` directory, but
there is no punning of project source/header file "root" dirs and `-I`
dirs.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
---
 .gitignore                                    |   6 +-
 Makefile                                      |   8 +--
 doc/internal-api/doxygen.cfg.in               |  12 ++--
 doc/manual/src/contributing/testing.md        |  65 ++++++++++++++----
 flake.nix                                     |   2 +-
 mk/common-test.sh                             |   2 +-
 src/libexpr/tests/local.mk                    |  19 -----
 .../common-protocol/content-address.bin       | Bin
 .../libstore/common-protocol/drv-output.bin   | Bin
 .../optional-content-address.bin              | Bin
 .../common-protocol/optional-store-path.bin   | Bin
 .../libstore/common-protocol/realisation.bin  | Bin
 .../data}/libstore/common-protocol/set.bin    | Bin
 .../libstore/common-protocol/store-path.bin   | Bin
 .../data}/libstore/common-protocol/string.bin | Bin
 .../data}/libstore/common-protocol/vector.bin | Bin
 .../derivation/bad-old-version-dyn-deps.drv   |   0
 .../data}/libstore/derivation/bad-version.drv |   0
 .../libstore/derivation/dynDerivationDeps.drv |   0
 .../derivation/dynDerivationDeps.json         |   0
 .../derivation/output-caFixedFlat.json        |   0
 .../derivation/output-caFixedNAR.json         |   0
 .../derivation/output-caFixedText.json        |   0
 .../derivation/output-caFloating.json         |   0
 .../libstore/derivation/output-deferred.json  |   0
 .../libstore/derivation/output-impure.json    |   0
 .../derivation/output-inputAddressed.json     |   0
 .../unit/data}/libstore/derivation/simple.drv |   0
 .../data}/libstore/derivation/simple.json     |   0
 .../unit/data}/libstore/nar-info/impure.json  |   0
 .../unit/data}/libstore/nar-info/pure.json    |   0
 .../unit/data}/libstore/path-info/impure.json |   0
 .../unit/data}/libstore/path-info/pure.json   |   0
 .../serve-protocol/build-result-2.2.bin       | Bin
 .../serve-protocol/build-result-2.3.bin       | Bin
 .../serve-protocol/build-result-2.6.bin       | Bin
 .../serve-protocol/content-address.bin        | Bin
 .../libstore/serve-protocol/drv-output.bin    | Bin
 .../optional-content-address.bin              | Bin
 .../serve-protocol/optional-store-path.bin    | Bin
 .../libstore/serve-protocol/realisation.bin   | Bin
 .../data}/libstore/serve-protocol/set.bin     | Bin
 .../libstore/serve-protocol/store-path.bin    | Bin
 .../data}/libstore/serve-protocol/string.bin  | Bin
 .../data}/libstore/serve-protocol/vector.bin  | Bin
 .../worker-protocol/build-result-1.27.bin     | Bin
 .../worker-protocol/build-result-1.28.bin     | Bin
 .../worker-protocol/build-result-1.29.bin     | Bin
 .../worker-protocol/content-address.bin       | Bin
 .../worker-protocol/derived-path-1.29.bin     | Bin
 .../worker-protocol/derived-path-1.30.bin     | Bin
 .../libstore/worker-protocol/drv-output.bin   | Bin
 .../keyed-build-result-1.29.bin               | Bin
 .../optional-content-address.bin              | Bin
 .../worker-protocol/optional-store-path.bin   | Bin
 .../worker-protocol/optional-trusted-flag.bin | Bin
 .../libstore/worker-protocol/realisation.bin  | Bin
 .../data}/libstore/worker-protocol/set.bin    | Bin
 .../libstore/worker-protocol/store-path.bin   | Bin
 .../data}/libstore/worker-protocol/string.bin | Bin
 .../unkeyed-valid-path-info-1.15.bin          | Bin
 .../worker-protocol/valid-path-info-1.15.bin  | Bin
 .../worker-protocol/valid-path-info-1.16.bin  | Bin
 .../data}/libstore/worker-protocol/vector.bin | Bin
 .../unit/data}/libutil/git/check-data.sh      |   2 +-
 .../data}/libutil/git/hello-world-blob.bin    | Bin
 .../unit/data}/libutil/git/hello-world.bin    | Bin
 .../unit/data}/libutil/git/tree.bin           | Bin
 .../unit/data}/libutil/git/tree.txt           |   0
 tests/unit/libexpr/local.mk                   |  28 ++++++++
 .../unit}/libexpr/tests/derived-path.cc       |   0
 .../unit}/libexpr/tests/error_traces.cc       |   0
 {src => tests/unit}/libexpr/tests/flakeref.cc |   0
 {src => tests/unit}/libexpr/tests/json.cc     |   0
 {src => tests/unit}/libexpr/tests/libexpr.hh  |   0
 {src => tests/unit}/libexpr/tests/primops.cc  |   0
 .../unit}/libexpr/tests/search-path.cc        |   0
 {src => tests/unit}/libexpr/tests/trivial.cc  |   0
 .../unit}/libexpr/tests/value/context.hh      |   2 +-
 .../unit}/libexpr/tests/value/print.cc        |   0
 .../unit/libexpr}/value/context.cc            |   0
 .../tests => tests/unit/libstore}/local.mk    |  12 +++-
 .../libstore}/test-data/machines.bad_format   |   0
 .../unit/libstore}/test-data/machines.valid   |   0
 .../unit}/libstore/tests/common-protocol.cc   |   0
 .../unit}/libstore/tests/derivation.cc        |   0
 .../unit}/libstore/tests/derived-path.cc      |   0
 .../unit}/libstore/tests/derived-path.hh      |   0
 .../libstore/tests/downstream-placeholder.cc  |   0
 .../unit}/libstore/tests/libstore.hh          |   0
 .../unit}/libstore/tests/machines.cc          |   4 +-
 .../libstore/tests/nar-info-disk-cache.cc     |   0
 .../unit}/libstore/tests/nar-info.cc          |   0
 .../unit}/libstore/tests/outputs-spec.cc      |   2 +-
 .../unit}/libstore/tests/outputs-spec.hh      |   2 +-
 .../unit}/libstore/tests/path-info.cc         |   0
 {src => tests/unit}/libstore/tests/path.cc    |   0
 {src => tests/unit}/libstore/tests/path.hh    |   0
 .../unit}/libstore/tests/protocol.hh          |   0
 .../unit}/libstore/tests/references.cc        |   0
 .../unit}/libstore/tests/serve-protocol.cc    |   0
 .../unit}/libstore/tests/worker-protocol.cc   |   0
 .../tests => tests/unit/libutil}/local.mk     |  10 +--
 {src => tests/unit}/libutil/tests/args.cc     |   6 +-
 .../unit}/libutil/tests/canon-path.cc         |   0
 .../unit}/libutil/tests/characterization.hh   |   2 +-
 .../unit}/libutil/tests/chunked-vector.cc     |   0
 {src => tests/unit}/libutil/tests/closure.cc  |   0
 .../unit}/libutil/tests/compression.cc        |   0
 {src => tests/unit}/libutil/tests/config.cc   |   0
 {src => tests/unit}/libutil/tests/git.cc      |   2 +-
 {src => tests/unit}/libutil/tests/hash.cc     |   2 +-
 {src => tests/unit}/libutil/tests/hash.hh     |   0
 {src => tests/unit}/libutil/tests/hilite.cc   |   0
 {src => tests/unit}/libutil/tests/logging.cc  |   0
 .../unit}/libutil/tests/lru-cache.cc          |   0
 {src => tests/unit}/libutil/tests/pool.cc     |   0
 .../unit}/libutil/tests/references.cc         |   0
 .../unit}/libutil/tests/suggestions.cc        |   0
 {src => tests/unit}/libutil/tests/tests.cc    |   0
 {src => tests/unit}/libutil/tests/url.cc      |   0
 .../unit}/libutil/tests/xml-writer.cc         |   0
 122 files changed, 123 insertions(+), 65 deletions(-)
 delete mode 100644 src/libexpr/tests/local.mk
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/drv-output.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/optional-content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/optional-store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/realisation.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/set.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/string.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/common-protocol/vector.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/bad-old-version-dyn-deps.drv (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/bad-version.drv (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/dynDerivationDeps.drv (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/dynDerivationDeps.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-caFixedFlat.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-caFixedNAR.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-caFixedText.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-caFloating.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-deferred.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-impure.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/output-inputAddressed.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/simple.drv (100%)
 rename {unit-test-data => tests/unit/data}/libstore/derivation/simple.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/nar-info/impure.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/nar-info/pure.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/path-info/impure.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/path-info/pure.json (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/build-result-2.2.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/build-result-2.3.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/build-result-2.6.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/drv-output.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/optional-content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/optional-store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/realisation.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/set.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/string.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/serve-protocol/vector.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/build-result-1.27.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/build-result-1.28.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/build-result-1.29.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/derived-path-1.29.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/derived-path-1.30.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/drv-output.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/keyed-build-result-1.29.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/optional-content-address.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/optional-store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/optional-trusted-flag.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/realisation.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/set.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/store-path.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/string.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/unkeyed-valid-path-info-1.15.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/valid-path-info-1.15.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/valid-path-info-1.16.bin (100%)
 rename {unit-test-data => tests/unit/data}/libstore/worker-protocol/vector.bin (100%)
 rename {unit-test-data => tests/unit/data}/libutil/git/check-data.sh (98%)
 rename {unit-test-data => tests/unit/data}/libutil/git/hello-world-blob.bin (100%)
 rename {unit-test-data => tests/unit/data}/libutil/git/hello-world.bin (100%)
 rename {unit-test-data => tests/unit/data}/libutil/git/tree.bin (100%)
 rename {unit-test-data => tests/unit/data}/libutil/git/tree.txt (100%)
 create mode 100644 tests/unit/libexpr/local.mk
 rename {src => tests/unit}/libexpr/tests/derived-path.cc (100%)
 rename {src => tests/unit}/libexpr/tests/error_traces.cc (100%)
 rename {src => tests/unit}/libexpr/tests/flakeref.cc (100%)
 rename {src => tests/unit}/libexpr/tests/json.cc (100%)
 rename {src => tests/unit}/libexpr/tests/libexpr.hh (100%)
 rename {src => tests/unit}/libexpr/tests/primops.cc (100%)
 rename {src => tests/unit}/libexpr/tests/search-path.cc (100%)
 rename {src => tests/unit}/libexpr/tests/trivial.cc (100%)
 rename {src => tests/unit}/libexpr/tests/value/context.hh (95%)
 rename {src => tests/unit}/libexpr/tests/value/print.cc (100%)
 rename {src/libexpr/tests => tests/unit/libexpr}/value/context.cc (100%)
 rename {src/libstore/tests => tests/unit/libstore}/local.mk (64%)
 rename {src/libstore/tests => tests/unit/libstore}/test-data/machines.bad_format (100%)
 rename {src/libstore/tests => tests/unit/libstore}/test-data/machines.valid (100%)
 rename {src => tests/unit}/libstore/tests/common-protocol.cc (100%)
 rename {src => tests/unit}/libstore/tests/derivation.cc (100%)
 rename {src => tests/unit}/libstore/tests/derived-path.cc (100%)
 rename {src => tests/unit}/libstore/tests/derived-path.hh (100%)
 rename {src => tests/unit}/libstore/tests/downstream-placeholder.cc (100%)
 rename {src => tests/unit}/libstore/tests/libstore.hh (100%)
 rename {src => tests/unit}/libstore/tests/machines.cc (97%)
 rename {src => tests/unit}/libstore/tests/nar-info-disk-cache.cc (100%)
 rename {src => tests/unit}/libstore/tests/nar-info.cc (100%)
 rename {src => tests/unit}/libstore/tests/outputs-spec.cc (99%)
 rename {src => tests/unit}/libstore/tests/outputs-spec.hh (89%)
 rename {src => tests/unit}/libstore/tests/path-info.cc (100%)
 rename {src => tests/unit}/libstore/tests/path.cc (100%)
 rename {src => tests/unit}/libstore/tests/path.hh (100%)
 rename {src => tests/unit}/libstore/tests/protocol.hh (100%)
 rename {src => tests/unit}/libstore/tests/references.cc (100%)
 rename {src => tests/unit}/libstore/tests/serve-protocol.cc (100%)
 rename {src => tests/unit}/libstore/tests/worker-protocol.cc (100%)
 rename {src/libutil/tests => tests/unit/libutil}/local.mk (64%)
 rename {src => tests/unit}/libutil/tests/args.cc (98%)
 rename {src => tests/unit}/libutil/tests/canon-path.cc (100%)
 rename {src => tests/unit}/libutil/tests/characterization.hh (97%)
 rename {src => tests/unit}/libutil/tests/chunked-vector.cc (100%)
 rename {src => tests/unit}/libutil/tests/closure.cc (100%)
 rename {src => tests/unit}/libutil/tests/compression.cc (100%)
 rename {src => tests/unit}/libutil/tests/config.cc (100%)
 rename {src => tests/unit}/libutil/tests/git.cc (99%)
 rename {src => tests/unit}/libutil/tests/hash.cc (99%)
 rename {src => tests/unit}/libutil/tests/hash.hh (100%)
 rename {src => tests/unit}/libutil/tests/hilite.cc (100%)
 rename {src => tests/unit}/libutil/tests/logging.cc (100%)
 rename {src => tests/unit}/libutil/tests/lru-cache.cc (100%)
 rename {src => tests/unit}/libutil/tests/pool.cc (100%)
 rename {src => tests/unit}/libutil/tests/references.cc (100%)
 rename {src => tests/unit}/libutil/tests/suggestions.cc (100%)
 rename {src => tests/unit}/libutil/tests/tests.cc (100%)
 rename {src => tests/unit}/libutil/tests/url.cc (100%)
 rename {src => tests/unit}/libutil/tests/xml-writer.cc (100%)

diff --git a/.gitignore b/.gitignore
index 04d96ca2c091..23ba1077f68c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,14 +41,14 @@ perl/Makefile.config
 /src/libexpr/parser-tab.hh
 /src/libexpr/parser-tab.output
 /src/libexpr/nix.tbl
-/src/libexpr/tests/libnixexpr-tests
+/tests/unit/libexpr/libnixexpr-tests
 
 # /src/libstore/
 *.gen.*
-/src/libstore/tests/libnixstore-tests
+/tests/unit/libstore/libnixstore-tests
 
 # /src/libutil/
-/src/libutil/tests/libnixutil-tests
+/tests/unit/libutil/libnixutil-tests
 
 /src/nix/nix
 
diff --git a/Makefile b/Makefile
index 4f4ac0c6e295..87283fb335cf 100644
--- a/Makefile
+++ b/Makefile
@@ -25,11 +25,11 @@ makefiles = \
 endif
 
 ifeq ($(ENABLE_BUILD)_$(ENABLE_TESTS), yes_yes)
-UNIT_TEST_ENV = _NIX_TEST_UNIT_DATA=unit-test-data
+UNIT_TEST_ENV = _NIX_TEST_UNIT_DATA=tests/unit/data
 makefiles += \
-  src/libutil/tests/local.mk \
-  src/libstore/tests/local.mk \
-  src/libexpr/tests/local.mk
+  tests/unit/libutil/local.mk \
+  tests/unit/libstore/local.mk \
+  tests/unit/libexpr/local.mk
 endif
 
 ifeq ($(ENABLE_TESTS), yes)
diff --git a/doc/internal-api/doxygen.cfg.in b/doc/internal-api/doxygen.cfg.in
index 599be2470b8f..ad5af97e6fe9 100644
--- a/doc/internal-api/doxygen.cfg.in
+++ b/doc/internal-api/doxygen.cfg.in
@@ -39,17 +39,21 @@ INPUT                  = \
   src/libcmd \
   src/libexpr \
   src/libexpr/flake \
-  src/libexpr/tests \
-  src/libexpr/tests/value \
+  tests/unit/libexpr \
+  tests/unit/libexpr/value \
+  tests/unit/libexpr/test \
+  tests/unit/libexpr/test/value \
   src/libexpr/value \
   src/libfetchers \
   src/libmain \
   src/libstore \
   src/libstore/build \
   src/libstore/builtins \
-  src/libstore/tests \
+  tests/unit/libstore \
+  tests/unit/libstore/test \
   src/libutil \
-  src/libutil/tests \
+  tests/unit/libutil \
+  tests/unit/libutil/test \
   src/nix \
   src/nix-env \
   src/nix-store
diff --git a/doc/manual/src/contributing/testing.md b/doc/manual/src/contributing/testing.md
index 0b45b88a3239..42a4d6e15c37 100644
--- a/doc/manual/src/contributing/testing.md
+++ b/doc/manual/src/contributing/testing.md
@@ -30,32 +30,69 @@ The unit tests are defined using the [googletest] and [rapidcheck] frameworks.
 > ├── libexpr
 > │   ├── value/context.hh
 > │   ├── value/context.cc
+> │   …
+> │
+> ├── tests
 > │   │
 > │   …
->     └── tests
-> │       ├── value/context.hh
-> │       ├── value/context.cc
+> │   └── unit
+> │       ├── libutil
+> │       │   │
+> │       │   …
 > │       │
+> │       ├── libexpr
+> │       │   └── test
+> │       │       ├── value/context.hh
+> │       │       ├── value/context.cc
+> │       │       …
 > │       …
-> │
-> ├── unit-test-data
-> │   ├── libstore
-> │   │   ├── worker-protocol/content-address.bin
-> │   │   …
-> │   …
+> │       └── data
+> │           ├── libutil
+> │           │   ├── git/tree.txt
+> │           │   …
+> │           ├── libexpr
+> │           │   │
+> │           │   …
+> │           …
 > …
 > ```
 
-The unit tests for each Nix library (`libnixexpr`, `libnixstore`, etc..) live inside a directory `src/${library_shortname}/tests` within the directory for the library (`src/${library_shortname}`).
+The tests for each Nix library (`libnixexpr`, `libnixstore`, etc..) live inside a directory `src/${library_name_without-nix}-tests` next to the directory for the library (`src/${library_name_without-nix}`).
+Given a interface (header) and implementation pair in the original library, say, `libexpr/value/context.{hh,cc}`, we write tests for it in `libexpr-tests/value/context.cc`, and (possibly) declare additional interfaces for testing purposes in `libexpr-tests/test/value/context.hh`.
+
+> **Note**
+>
+> Only the extra header is nested inside the `test` directory. This is explained further below.
 
-The data is in `unit-test-data`, with one subdir per library, with the same name as where the code goes.
-For example, `libnixstore` code is in `src/libstore`, and its test data is in `unit-test-data/libstore`.
-The path to the `unit-test-data` directory is passed to the unit test executable with the environment variable `_NIX_TEST_UNIT_DATA`.
+The data is in `tests/unit/data`, with one subdir per library, with the same name as where the code goes.
+For example, `libnixstore` code is in `src/libstore`, and its test data is in `tests/unit/data/libstore`.
+The path to the `tests/unit/data` directory is passed to the unit test executable with the environment variable `_NIX_TEST_UNIT_DATA`.
 
 > **Note**
 > Due to the way googletest works, downstream unit test executables will actually include and re-run upstream library tests.
 > Therefore it is important that the same value for `_NIX_TEST_UNIT_DATA` be used with the tests for each library.
-> That is why we have the test data nested within a single `unit-test-data` directory.
+> That is why we have the test data nested within a single `tests/unit/data` directory.
+
+### Rationale
+
+The use of a separate directory for the unit tests might seem inconvenient, as the tests are not "right next to" the part of the code they are testing.
+But organizing the tests this way has one big benefit:
+there is no risk of any build-system wildcards for the library accidentally picking up test code that shoud not built and installed as part of the library.
+
+Likewise, the use of the `test/` subdir might seem superfluous:
+Isn't the point of the `*-test` subdir to indicate that these files are tests?
+Why do we need another `test` subdirectory?
+The answer is that we need to be able to tell apart the two headers, and make sure we include the right one.
+For `.cc` files, this is matter of doing `#include "foo.hh"` vs `#include "tests/foo.hh`
+For `.hh` files, this is a bit more subtle, because a `#include "foo.hh` instead `test/foo.hh` will end up including itself because `#include "..."`
+[always prioritizes files in the same directory](https://pubs.opengroup.org/onlinepubs/9699919799/utilities/c99.html#tag_20_11_04), rather than the original header from the library.
+Instead, use `#include <foo.hh>` to get the original library header, and `#include "tests/foo.hh"` to get the test header.
+
+Why do we have test headers at all?
+These are usually for [rapidcheck]'s `Arbitrary` machinery, which is used to describe how to generate values of a given type for the sake of running property tests.
+Because types contain other types, `Arbitrary` "instances" for some type are not just useful for testing that type, but also any other type that contains it.
+Indeed, if we don't reuse the upstream type's `Arbitrary` instance, the downstream type's `Arbitrary` instance would become much more complex and hard to understand.
+In order to reuse these instances, we therefore declare them in these testing headers.
 
 ### Running tests
 
diff --git a/flake.nix b/flake.nix
index 51d8184233a4..fd6e5c25e0d2 100644
--- a/flake.nix
+++ b/flake.nix
@@ -91,7 +91,7 @@
           ./misc
           ./precompiled-headers.h
           ./src
-          ./unit-test-data
+          ./tests/unit
           ./COPYING
           ./scripts/local.mk
           functionalTestFiles
diff --git a/mk/common-test.sh b/mk/common-test.sh
index 00ccd1584239..f493fb2bab37 100644
--- a/mk/common-test.sh
+++ b/mk/common-test.sh
@@ -1,7 +1,7 @@
 # Remove overall test dir (at most one of the two should match) and
 # remove file extension.
 test_name=$(echo -n "$test" | sed \
-    -e "s|^unit-test-data/||" \
+    -e "s|^tests/unit/data/||" \
     -e "s|^tests/functional/||" \
     -e "s|\.sh$||" \
     )
diff --git a/src/libexpr/tests/local.mk b/src/libexpr/tests/local.mk
deleted file mode 100644
index 331a5ead60e4..000000000000
--- a/src/libexpr/tests/local.mk
+++ /dev/null
@@ -1,19 +0,0 @@
-check: libexpr-tests_RUN
-
-programs += libexpr-tests
-
-libexpr-tests_NAME := libnixexpr-tests
-
-libexpr-tests_DIR := $(d)
-
-libexpr-tests_INSTALL_DIR :=
-
-libexpr-tests_SOURCES := \
-    $(wildcard $(d)/*.cc) \
-    $(wildcard $(d)/value/*.cc)
-
-libexpr-tests_CXXFLAGS += -I src/libexpr -I src/libutil -I src/libstore -I src/libexpr/tests -I src/libfetchers
-
-libexpr-tests_LIBS = libstore-tests libutils-tests libexpr libutil libstore libfetchers
-
-libexpr-tests_LDFLAGS := $(GTEST_LIBS) -lgmock
diff --git a/unit-test-data/libstore/common-protocol/content-address.bin b/tests/unit/data/libstore/common-protocol/content-address.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/content-address.bin
rename to tests/unit/data/libstore/common-protocol/content-address.bin
diff --git a/unit-test-data/libstore/common-protocol/drv-output.bin b/tests/unit/data/libstore/common-protocol/drv-output.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/drv-output.bin
rename to tests/unit/data/libstore/common-protocol/drv-output.bin
diff --git a/unit-test-data/libstore/common-protocol/optional-content-address.bin b/tests/unit/data/libstore/common-protocol/optional-content-address.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/optional-content-address.bin
rename to tests/unit/data/libstore/common-protocol/optional-content-address.bin
diff --git a/unit-test-data/libstore/common-protocol/optional-store-path.bin b/tests/unit/data/libstore/common-protocol/optional-store-path.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/optional-store-path.bin
rename to tests/unit/data/libstore/common-protocol/optional-store-path.bin
diff --git a/unit-test-data/libstore/common-protocol/realisation.bin b/tests/unit/data/libstore/common-protocol/realisation.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/realisation.bin
rename to tests/unit/data/libstore/common-protocol/realisation.bin
diff --git a/unit-test-data/libstore/common-protocol/set.bin b/tests/unit/data/libstore/common-protocol/set.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/set.bin
rename to tests/unit/data/libstore/common-protocol/set.bin
diff --git a/unit-test-data/libstore/common-protocol/store-path.bin b/tests/unit/data/libstore/common-protocol/store-path.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/store-path.bin
rename to tests/unit/data/libstore/common-protocol/store-path.bin
diff --git a/unit-test-data/libstore/common-protocol/string.bin b/tests/unit/data/libstore/common-protocol/string.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/string.bin
rename to tests/unit/data/libstore/common-protocol/string.bin
diff --git a/unit-test-data/libstore/common-protocol/vector.bin b/tests/unit/data/libstore/common-protocol/vector.bin
similarity index 100%
rename from unit-test-data/libstore/common-protocol/vector.bin
rename to tests/unit/data/libstore/common-protocol/vector.bin
diff --git a/unit-test-data/libstore/derivation/bad-old-version-dyn-deps.drv b/tests/unit/data/libstore/derivation/bad-old-version-dyn-deps.drv
similarity index 100%
rename from unit-test-data/libstore/derivation/bad-old-version-dyn-deps.drv
rename to tests/unit/data/libstore/derivation/bad-old-version-dyn-deps.drv
diff --git a/unit-test-data/libstore/derivation/bad-version.drv b/tests/unit/data/libstore/derivation/bad-version.drv
similarity index 100%
rename from unit-test-data/libstore/derivation/bad-version.drv
rename to tests/unit/data/libstore/derivation/bad-version.drv
diff --git a/unit-test-data/libstore/derivation/dynDerivationDeps.drv b/tests/unit/data/libstore/derivation/dynDerivationDeps.drv
similarity index 100%
rename from unit-test-data/libstore/derivation/dynDerivationDeps.drv
rename to tests/unit/data/libstore/derivation/dynDerivationDeps.drv
diff --git a/unit-test-data/libstore/derivation/dynDerivationDeps.json b/tests/unit/data/libstore/derivation/dynDerivationDeps.json
similarity index 100%
rename from unit-test-data/libstore/derivation/dynDerivationDeps.json
rename to tests/unit/data/libstore/derivation/dynDerivationDeps.json
diff --git a/unit-test-data/libstore/derivation/output-caFixedFlat.json b/tests/unit/data/libstore/derivation/output-caFixedFlat.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-caFixedFlat.json
rename to tests/unit/data/libstore/derivation/output-caFixedFlat.json
diff --git a/unit-test-data/libstore/derivation/output-caFixedNAR.json b/tests/unit/data/libstore/derivation/output-caFixedNAR.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-caFixedNAR.json
rename to tests/unit/data/libstore/derivation/output-caFixedNAR.json
diff --git a/unit-test-data/libstore/derivation/output-caFixedText.json b/tests/unit/data/libstore/derivation/output-caFixedText.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-caFixedText.json
rename to tests/unit/data/libstore/derivation/output-caFixedText.json
diff --git a/unit-test-data/libstore/derivation/output-caFloating.json b/tests/unit/data/libstore/derivation/output-caFloating.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-caFloating.json
rename to tests/unit/data/libstore/derivation/output-caFloating.json
diff --git a/unit-test-data/libstore/derivation/output-deferred.json b/tests/unit/data/libstore/derivation/output-deferred.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-deferred.json
rename to tests/unit/data/libstore/derivation/output-deferred.json
diff --git a/unit-test-data/libstore/derivation/output-impure.json b/tests/unit/data/libstore/derivation/output-impure.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-impure.json
rename to tests/unit/data/libstore/derivation/output-impure.json
diff --git a/unit-test-data/libstore/derivation/output-inputAddressed.json b/tests/unit/data/libstore/derivation/output-inputAddressed.json
similarity index 100%
rename from unit-test-data/libstore/derivation/output-inputAddressed.json
rename to tests/unit/data/libstore/derivation/output-inputAddressed.json
diff --git a/unit-test-data/libstore/derivation/simple.drv b/tests/unit/data/libstore/derivation/simple.drv
similarity index 100%
rename from unit-test-data/libstore/derivation/simple.drv
rename to tests/unit/data/libstore/derivation/simple.drv
diff --git a/unit-test-data/libstore/derivation/simple.json b/tests/unit/data/libstore/derivation/simple.json
similarity index 100%
rename from unit-test-data/libstore/derivation/simple.json
rename to tests/unit/data/libstore/derivation/simple.json
diff --git a/unit-test-data/libstore/nar-info/impure.json b/tests/unit/data/libstore/nar-info/impure.json
similarity index 100%
rename from unit-test-data/libstore/nar-info/impure.json
rename to tests/unit/data/libstore/nar-info/impure.json
diff --git a/unit-test-data/libstore/nar-info/pure.json b/tests/unit/data/libstore/nar-info/pure.json
similarity index 100%
rename from unit-test-data/libstore/nar-info/pure.json
rename to tests/unit/data/libstore/nar-info/pure.json
diff --git a/unit-test-data/libstore/path-info/impure.json b/tests/unit/data/libstore/path-info/impure.json
similarity index 100%
rename from unit-test-data/libstore/path-info/impure.json
rename to tests/unit/data/libstore/path-info/impure.json
diff --git a/unit-test-data/libstore/path-info/pure.json b/tests/unit/data/libstore/path-info/pure.json
similarity index 100%
rename from unit-test-data/libstore/path-info/pure.json
rename to tests/unit/data/libstore/path-info/pure.json
diff --git a/unit-test-data/libstore/serve-protocol/build-result-2.2.bin b/tests/unit/data/libstore/serve-protocol/build-result-2.2.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/build-result-2.2.bin
rename to tests/unit/data/libstore/serve-protocol/build-result-2.2.bin
diff --git a/unit-test-data/libstore/serve-protocol/build-result-2.3.bin b/tests/unit/data/libstore/serve-protocol/build-result-2.3.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/build-result-2.3.bin
rename to tests/unit/data/libstore/serve-protocol/build-result-2.3.bin
diff --git a/unit-test-data/libstore/serve-protocol/build-result-2.6.bin b/tests/unit/data/libstore/serve-protocol/build-result-2.6.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/build-result-2.6.bin
rename to tests/unit/data/libstore/serve-protocol/build-result-2.6.bin
diff --git a/unit-test-data/libstore/serve-protocol/content-address.bin b/tests/unit/data/libstore/serve-protocol/content-address.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/content-address.bin
rename to tests/unit/data/libstore/serve-protocol/content-address.bin
diff --git a/unit-test-data/libstore/serve-protocol/drv-output.bin b/tests/unit/data/libstore/serve-protocol/drv-output.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/drv-output.bin
rename to tests/unit/data/libstore/serve-protocol/drv-output.bin
diff --git a/unit-test-data/libstore/serve-protocol/optional-content-address.bin b/tests/unit/data/libstore/serve-protocol/optional-content-address.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/optional-content-address.bin
rename to tests/unit/data/libstore/serve-protocol/optional-content-address.bin
diff --git a/unit-test-data/libstore/serve-protocol/optional-store-path.bin b/tests/unit/data/libstore/serve-protocol/optional-store-path.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/optional-store-path.bin
rename to tests/unit/data/libstore/serve-protocol/optional-store-path.bin
diff --git a/unit-test-data/libstore/serve-protocol/realisation.bin b/tests/unit/data/libstore/serve-protocol/realisation.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/realisation.bin
rename to tests/unit/data/libstore/serve-protocol/realisation.bin
diff --git a/unit-test-data/libstore/serve-protocol/set.bin b/tests/unit/data/libstore/serve-protocol/set.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/set.bin
rename to tests/unit/data/libstore/serve-protocol/set.bin
diff --git a/unit-test-data/libstore/serve-protocol/store-path.bin b/tests/unit/data/libstore/serve-protocol/store-path.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/store-path.bin
rename to tests/unit/data/libstore/serve-protocol/store-path.bin
diff --git a/unit-test-data/libstore/serve-protocol/string.bin b/tests/unit/data/libstore/serve-protocol/string.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/string.bin
rename to tests/unit/data/libstore/serve-protocol/string.bin
diff --git a/unit-test-data/libstore/serve-protocol/vector.bin b/tests/unit/data/libstore/serve-protocol/vector.bin
similarity index 100%
rename from unit-test-data/libstore/serve-protocol/vector.bin
rename to tests/unit/data/libstore/serve-protocol/vector.bin
diff --git a/unit-test-data/libstore/worker-protocol/build-result-1.27.bin b/tests/unit/data/libstore/worker-protocol/build-result-1.27.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/build-result-1.27.bin
rename to tests/unit/data/libstore/worker-protocol/build-result-1.27.bin
diff --git a/unit-test-data/libstore/worker-protocol/build-result-1.28.bin b/tests/unit/data/libstore/worker-protocol/build-result-1.28.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/build-result-1.28.bin
rename to tests/unit/data/libstore/worker-protocol/build-result-1.28.bin
diff --git a/unit-test-data/libstore/worker-protocol/build-result-1.29.bin b/tests/unit/data/libstore/worker-protocol/build-result-1.29.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/build-result-1.29.bin
rename to tests/unit/data/libstore/worker-protocol/build-result-1.29.bin
diff --git a/unit-test-data/libstore/worker-protocol/content-address.bin b/tests/unit/data/libstore/worker-protocol/content-address.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/content-address.bin
rename to tests/unit/data/libstore/worker-protocol/content-address.bin
diff --git a/unit-test-data/libstore/worker-protocol/derived-path-1.29.bin b/tests/unit/data/libstore/worker-protocol/derived-path-1.29.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/derived-path-1.29.bin
rename to tests/unit/data/libstore/worker-protocol/derived-path-1.29.bin
diff --git a/unit-test-data/libstore/worker-protocol/derived-path-1.30.bin b/tests/unit/data/libstore/worker-protocol/derived-path-1.30.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/derived-path-1.30.bin
rename to tests/unit/data/libstore/worker-protocol/derived-path-1.30.bin
diff --git a/unit-test-data/libstore/worker-protocol/drv-output.bin b/tests/unit/data/libstore/worker-protocol/drv-output.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/drv-output.bin
rename to tests/unit/data/libstore/worker-protocol/drv-output.bin
diff --git a/unit-test-data/libstore/worker-protocol/keyed-build-result-1.29.bin b/tests/unit/data/libstore/worker-protocol/keyed-build-result-1.29.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/keyed-build-result-1.29.bin
rename to tests/unit/data/libstore/worker-protocol/keyed-build-result-1.29.bin
diff --git a/unit-test-data/libstore/worker-protocol/optional-content-address.bin b/tests/unit/data/libstore/worker-protocol/optional-content-address.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/optional-content-address.bin
rename to tests/unit/data/libstore/worker-protocol/optional-content-address.bin
diff --git a/unit-test-data/libstore/worker-protocol/optional-store-path.bin b/tests/unit/data/libstore/worker-protocol/optional-store-path.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/optional-store-path.bin
rename to tests/unit/data/libstore/worker-protocol/optional-store-path.bin
diff --git a/unit-test-data/libstore/worker-protocol/optional-trusted-flag.bin b/tests/unit/data/libstore/worker-protocol/optional-trusted-flag.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/optional-trusted-flag.bin
rename to tests/unit/data/libstore/worker-protocol/optional-trusted-flag.bin
diff --git a/unit-test-data/libstore/worker-protocol/realisation.bin b/tests/unit/data/libstore/worker-protocol/realisation.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/realisation.bin
rename to tests/unit/data/libstore/worker-protocol/realisation.bin
diff --git a/unit-test-data/libstore/worker-protocol/set.bin b/tests/unit/data/libstore/worker-protocol/set.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/set.bin
rename to tests/unit/data/libstore/worker-protocol/set.bin
diff --git a/unit-test-data/libstore/worker-protocol/store-path.bin b/tests/unit/data/libstore/worker-protocol/store-path.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/store-path.bin
rename to tests/unit/data/libstore/worker-protocol/store-path.bin
diff --git a/unit-test-data/libstore/worker-protocol/string.bin b/tests/unit/data/libstore/worker-protocol/string.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/string.bin
rename to tests/unit/data/libstore/worker-protocol/string.bin
diff --git a/unit-test-data/libstore/worker-protocol/unkeyed-valid-path-info-1.15.bin b/tests/unit/data/libstore/worker-protocol/unkeyed-valid-path-info-1.15.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/unkeyed-valid-path-info-1.15.bin
rename to tests/unit/data/libstore/worker-protocol/unkeyed-valid-path-info-1.15.bin
diff --git a/unit-test-data/libstore/worker-protocol/valid-path-info-1.15.bin b/tests/unit/data/libstore/worker-protocol/valid-path-info-1.15.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/valid-path-info-1.15.bin
rename to tests/unit/data/libstore/worker-protocol/valid-path-info-1.15.bin
diff --git a/unit-test-data/libstore/worker-protocol/valid-path-info-1.16.bin b/tests/unit/data/libstore/worker-protocol/valid-path-info-1.16.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/valid-path-info-1.16.bin
rename to tests/unit/data/libstore/worker-protocol/valid-path-info-1.16.bin
diff --git a/unit-test-data/libstore/worker-protocol/vector.bin b/tests/unit/data/libstore/worker-protocol/vector.bin
similarity index 100%
rename from unit-test-data/libstore/worker-protocol/vector.bin
rename to tests/unit/data/libstore/worker-protocol/vector.bin
diff --git a/unit-test-data/libutil/git/check-data.sh b/tests/unit/data/libutil/git/check-data.sh
similarity index 98%
rename from unit-test-data/libutil/git/check-data.sh
rename to tests/unit/data/libutil/git/check-data.sh
index 68b705c95c6e..b3f59c4f12ab 100644
--- a/unit-test-data/libutil/git/check-data.sh
+++ b/tests/unit/data/libutil/git/check-data.sh
@@ -2,7 +2,7 @@
 
 set -eu -o pipefail
 
-export TEST_ROOT=$(realpath ${TMPDIR:-/tmp}/nix-test)/git-hashing/unit-test-data
+export TEST_ROOT=$(realpath ${TMPDIR:-/tmp}/nix-test)/git-hashing/check-data
 mkdir -p $TEST_ROOT
 
 repo="$TEST_ROOT/scratch"
diff --git a/unit-test-data/libutil/git/hello-world-blob.bin b/tests/unit/data/libutil/git/hello-world-blob.bin
similarity index 100%
rename from unit-test-data/libutil/git/hello-world-blob.bin
rename to tests/unit/data/libutil/git/hello-world-blob.bin
diff --git a/unit-test-data/libutil/git/hello-world.bin b/tests/unit/data/libutil/git/hello-world.bin
similarity index 100%
rename from unit-test-data/libutil/git/hello-world.bin
rename to tests/unit/data/libutil/git/hello-world.bin
diff --git a/unit-test-data/libutil/git/tree.bin b/tests/unit/data/libutil/git/tree.bin
similarity index 100%
rename from unit-test-data/libutil/git/tree.bin
rename to tests/unit/data/libutil/git/tree.bin
diff --git a/unit-test-data/libutil/git/tree.txt b/tests/unit/data/libutil/git/tree.txt
similarity index 100%
rename from unit-test-data/libutil/git/tree.txt
rename to tests/unit/data/libutil/git/tree.txt
diff --git a/tests/unit/libexpr/local.mk b/tests/unit/libexpr/local.mk
new file mode 100644
index 000000000000..b17a9fcd86c9
--- /dev/null
+++ b/tests/unit/libexpr/local.mk
@@ -0,0 +1,28 @@
+check: libexpr-tests_RUN
+
+programs += libexpr-tests
+
+libexpr-tests_NAME := libnixexpr-tests
+
+libexpr-tests_DIR := $(d)
+
+libexpr-tests_INSTALL_DIR :=
+
+libexpr-tests_SOURCES := \
+    $(wildcard $(d)/tests/*.cc) \
+    $(wildcard $(d)/tests/value/*.cc)
+
+libexpr-tests_CXXFLAGS += \
+    -I tests/unit/libexpr \
+    -I tests/unit/libstore \
+    -I tests/unit/libutil \
+    -I src/libexpr \
+    -I src/libfetchers \
+    -I src/libstore \
+    -I src/libutil
+
+libexpr-tests_LIBS = \
+    libstore-tests libutils-tests \
+    libexpr libfetchers libstore libutil
+
+libexpr-tests_LDFLAGS := $(GTEST_LIBS) -lgmock
diff --git a/src/libexpr/tests/derived-path.cc b/tests/unit/libexpr/tests/derived-path.cc
similarity index 100%
rename from src/libexpr/tests/derived-path.cc
rename to tests/unit/libexpr/tests/derived-path.cc
diff --git a/src/libexpr/tests/error_traces.cc b/tests/unit/libexpr/tests/error_traces.cc
similarity index 100%
rename from src/libexpr/tests/error_traces.cc
rename to tests/unit/libexpr/tests/error_traces.cc
diff --git a/src/libexpr/tests/flakeref.cc b/tests/unit/libexpr/tests/flakeref.cc
similarity index 100%
rename from src/libexpr/tests/flakeref.cc
rename to tests/unit/libexpr/tests/flakeref.cc
diff --git a/src/libexpr/tests/json.cc b/tests/unit/libexpr/tests/json.cc
similarity index 100%
rename from src/libexpr/tests/json.cc
rename to tests/unit/libexpr/tests/json.cc
diff --git a/src/libexpr/tests/libexpr.hh b/tests/unit/libexpr/tests/libexpr.hh
similarity index 100%
rename from src/libexpr/tests/libexpr.hh
rename to tests/unit/libexpr/tests/libexpr.hh
diff --git a/src/libexpr/tests/primops.cc b/tests/unit/libexpr/tests/primops.cc
similarity index 100%
rename from src/libexpr/tests/primops.cc
rename to tests/unit/libexpr/tests/primops.cc
diff --git a/src/libexpr/tests/search-path.cc b/tests/unit/libexpr/tests/search-path.cc
similarity index 100%
rename from src/libexpr/tests/search-path.cc
rename to tests/unit/libexpr/tests/search-path.cc
diff --git a/src/libexpr/tests/trivial.cc b/tests/unit/libexpr/tests/trivial.cc
similarity index 100%
rename from src/libexpr/tests/trivial.cc
rename to tests/unit/libexpr/tests/trivial.cc
diff --git a/src/libexpr/tests/value/context.hh b/tests/unit/libexpr/tests/value/context.hh
similarity index 95%
rename from src/libexpr/tests/value/context.hh
rename to tests/unit/libexpr/tests/value/context.hh
index c0bc97ba3c46..8c68c78bbd1c 100644
--- a/src/libexpr/tests/value/context.hh
+++ b/tests/unit/libexpr/tests/value/context.hh
@@ -3,7 +3,7 @@
 
 #include <rapidcheck/gen/Arbitrary.h>
 
-#include <value/context.hh>
+#include "value/context.hh"
 
 namespace rc {
 using namespace nix;
diff --git a/src/libexpr/tests/value/print.cc b/tests/unit/libexpr/tests/value/print.cc
similarity index 100%
rename from src/libexpr/tests/value/print.cc
rename to tests/unit/libexpr/tests/value/print.cc
diff --git a/src/libexpr/tests/value/context.cc b/tests/unit/libexpr/value/context.cc
similarity index 100%
rename from src/libexpr/tests/value/context.cc
rename to tests/unit/libexpr/value/context.cc
diff --git a/src/libstore/tests/local.mk b/tests/unit/libstore/local.mk
similarity index 64%
rename from src/libstore/tests/local.mk
rename to tests/unit/libstore/local.mk
index 03becc7d11b6..92ec8e355bf4 100644
--- a/src/libstore/tests/local.mk
+++ b/tests/unit/libstore/local.mk
@@ -20,10 +20,16 @@ libstore-tests_DIR := $(d)
 
 libstore-tests_INSTALL_DIR :=
 
-libstore-tests_SOURCES := $(wildcard $(d)/*.cc)
+libstore-tests_SOURCES := $(wildcard $(d)/tests/*.cc)
 
-libstore-tests_CXXFLAGS += -I src/libstore -I src/libutil
+libstore-tests_CXXFLAGS += \
+    -I tests/unit/libstore \
+    -I tests/unit/libutil \
+    -I src/libstore \
+    -I src/libutil
 
-libstore-tests_LIBS = libutil-tests libstore libutil
+libstore-tests_LIBS = \
+    libutil-tests \
+    libstore libutil
 
 libstore-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)
diff --git a/src/libstore/tests/test-data/machines.bad_format b/tests/unit/libstore/test-data/machines.bad_format
similarity index 100%
rename from src/libstore/tests/test-data/machines.bad_format
rename to tests/unit/libstore/test-data/machines.bad_format
diff --git a/src/libstore/tests/test-data/machines.valid b/tests/unit/libstore/test-data/machines.valid
similarity index 100%
rename from src/libstore/tests/test-data/machines.valid
rename to tests/unit/libstore/test-data/machines.valid
diff --git a/src/libstore/tests/common-protocol.cc b/tests/unit/libstore/tests/common-protocol.cc
similarity index 100%
rename from src/libstore/tests/common-protocol.cc
rename to tests/unit/libstore/tests/common-protocol.cc
diff --git a/src/libstore/tests/derivation.cc b/tests/unit/libstore/tests/derivation.cc
similarity index 100%
rename from src/libstore/tests/derivation.cc
rename to tests/unit/libstore/tests/derivation.cc
diff --git a/src/libstore/tests/derived-path.cc b/tests/unit/libstore/tests/derived-path.cc
similarity index 100%
rename from src/libstore/tests/derived-path.cc
rename to tests/unit/libstore/tests/derived-path.cc
diff --git a/src/libstore/tests/derived-path.hh b/tests/unit/libstore/tests/derived-path.hh
similarity index 100%
rename from src/libstore/tests/derived-path.hh
rename to tests/unit/libstore/tests/derived-path.hh
diff --git a/src/libstore/tests/downstream-placeholder.cc b/tests/unit/libstore/tests/downstream-placeholder.cc
similarity index 100%
rename from src/libstore/tests/downstream-placeholder.cc
rename to tests/unit/libstore/tests/downstream-placeholder.cc
diff --git a/src/libstore/tests/libstore.hh b/tests/unit/libstore/tests/libstore.hh
similarity index 100%
rename from src/libstore/tests/libstore.hh
rename to tests/unit/libstore/tests/libstore.hh
diff --git a/src/libstore/tests/machines.cc b/tests/unit/libstore/tests/machines.cc
similarity index 97%
rename from src/libstore/tests/machines.cc
rename to tests/unit/libstore/tests/machines.cc
index fede328ea3f3..5b66e5a5be93 100644
--- a/src/libstore/tests/machines.cc
+++ b/tests/unit/libstore/tests/machines.cc
@@ -139,7 +139,7 @@ TEST(machines, getMachinesWithIncorrectFormat) {
 }
 
 TEST(machines, getMachinesWithCorrectFileReference) {
-    auto path = absPath("src/libstore/tests/test-data/machines.valid");
+    auto path = absPath("tests/unit/libstore/test-data/machines.valid");
     ASSERT_TRUE(pathExists(path));
 
     settings.builders = std::string("@") + path;
@@ -166,6 +166,6 @@ TEST(machines, getMachinesWithIncorrectFileReference) {
 }
 
 TEST(machines, getMachinesWithCorrectFileReferenceToIncorrectFile) {
-    settings.builders = std::string("@") + absPath("src/libstore/tests/test-data/machines.bad_format");
+    settings.builders = std::string("@") + absPath("tests/unit/libstore/test-data/machines.bad_format");
     EXPECT_THROW(getMachines(), FormatError);
 }
diff --git a/src/libstore/tests/nar-info-disk-cache.cc b/tests/unit/libstore/tests/nar-info-disk-cache.cc
similarity index 100%
rename from src/libstore/tests/nar-info-disk-cache.cc
rename to tests/unit/libstore/tests/nar-info-disk-cache.cc
diff --git a/src/libstore/tests/nar-info.cc b/tests/unit/libstore/tests/nar-info.cc
similarity index 100%
rename from src/libstore/tests/nar-info.cc
rename to tests/unit/libstore/tests/nar-info.cc
diff --git a/src/libstore/tests/outputs-spec.cc b/tests/unit/libstore/tests/outputs-spec.cc
similarity index 99%
rename from src/libstore/tests/outputs-spec.cc
rename to tests/unit/libstore/tests/outputs-spec.cc
index 95294518544b..214afda4e34c 100644
--- a/src/libstore/tests/outputs-spec.cc
+++ b/tests/unit/libstore/tests/outputs-spec.cc
@@ -1,4 +1,4 @@
-#include "outputs-spec.hh"
+#include "tests/outputs-spec.hh"
 
 #include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
diff --git a/src/libstore/tests/outputs-spec.hh b/tests/unit/libstore/tests/outputs-spec.hh
similarity index 89%
rename from src/libstore/tests/outputs-spec.hh
rename to tests/unit/libstore/tests/outputs-spec.hh
index ded331b333e3..f5bf9042d201 100644
--- a/src/libstore/tests/outputs-spec.hh
+++ b/tests/unit/libstore/tests/outputs-spec.hh
@@ -5,7 +5,7 @@
 
 #include <outputs-spec.hh>
 
-#include <tests/path.hh>
+#include "tests/path.hh"
 
 namespace rc {
 using namespace nix;
diff --git a/src/libstore/tests/path-info.cc b/tests/unit/libstore/tests/path-info.cc
similarity index 100%
rename from src/libstore/tests/path-info.cc
rename to tests/unit/libstore/tests/path-info.cc
diff --git a/src/libstore/tests/path.cc b/tests/unit/libstore/tests/path.cc
similarity index 100%
rename from src/libstore/tests/path.cc
rename to tests/unit/libstore/tests/path.cc
diff --git a/src/libstore/tests/path.hh b/tests/unit/libstore/tests/path.hh
similarity index 100%
rename from src/libstore/tests/path.hh
rename to tests/unit/libstore/tests/path.hh
diff --git a/src/libstore/tests/protocol.hh b/tests/unit/libstore/tests/protocol.hh
similarity index 100%
rename from src/libstore/tests/protocol.hh
rename to tests/unit/libstore/tests/protocol.hh
diff --git a/src/libstore/tests/references.cc b/tests/unit/libstore/tests/references.cc
similarity index 100%
rename from src/libstore/tests/references.cc
rename to tests/unit/libstore/tests/references.cc
diff --git a/src/libstore/tests/serve-protocol.cc b/tests/unit/libstore/tests/serve-protocol.cc
similarity index 100%
rename from src/libstore/tests/serve-protocol.cc
rename to tests/unit/libstore/tests/serve-protocol.cc
diff --git a/src/libstore/tests/worker-protocol.cc b/tests/unit/libstore/tests/worker-protocol.cc
similarity index 100%
rename from src/libstore/tests/worker-protocol.cc
rename to tests/unit/libstore/tests/worker-protocol.cc
diff --git a/src/libutil/tests/local.mk b/tests/unit/libutil/local.mk
similarity index 64%
rename from src/libutil/tests/local.mk
rename to tests/unit/libutil/local.mk
index 5a970c0f20b3..a6462ae117f8 100644
--- a/src/libutil/tests/local.mk
+++ b/tests/unit/libutil/local.mk
@@ -20,14 +20,16 @@ libutil-tests_DIR := $(d)
 
 libutil-tests_INSTALL_DIR :=
 
-libutil-tests_SOURCES := $(wildcard $(d)/*.cc)
+libutil-tests_SOURCES := $(wildcard $(d)/tests/*.cc)
 
-libutil-tests_CXXFLAGS += -I src/libutil
+libutil-tests_CXXFLAGS += \
+    -I tests/unit/libutil \
+    -I src/libutil
 
 libutil-tests_LIBS = libutil
 
 libutil-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)
 
-check: unit-test-data/libutil/git/check-data.sh.test
+check: tests/unit/data/libutil/git/check-data.sh.test
 
-$(eval $(call run-test,unit-test-data/libutil/git/check-data.sh))
+$(eval $(call run-test,tests/unit/data/libutil/git/check-data.sh))
diff --git a/src/libutil/tests/args.cc b/tests/unit/libutil/tests/args.cc
similarity index 98%
rename from src/libutil/tests/args.cc
rename to tests/unit/libutil/tests/args.cc
index bea74a8c8393..950224430065 100644
--- a/src/libutil/tests/args.cc
+++ b/tests/unit/libutil/tests/args.cc
@@ -1,5 +1,5 @@
-#include "../args.hh"
-#include "libutil/fs-sink.hh"
+#include "args.hh"
+#include "fs-sink.hh"
 #include <list>
 
 #include <gtest/gtest.h>
@@ -165,4 +165,4 @@ RC_GTEST_PROP(
 
 #endif
 
-}
\ No newline at end of file
+}
diff --git a/src/libutil/tests/canon-path.cc b/tests/unit/libutil/tests/canon-path.cc
similarity index 100%
rename from src/libutil/tests/canon-path.cc
rename to tests/unit/libutil/tests/canon-path.cc
diff --git a/src/libutil/tests/characterization.hh b/tests/unit/libutil/tests/characterization.hh
similarity index 97%
rename from src/libutil/tests/characterization.hh
rename to tests/unit/libutil/tests/characterization.hh
index 6eb513d68746..1a897bb5f2a5 100644
--- a/src/libutil/tests/characterization.hh
+++ b/tests/unit/libutil/tests/characterization.hh
@@ -9,7 +9,7 @@
 namespace nix {
 
 /**
- * The path to the `unit-test-data` directory. See the contributing
+ * The path to the `tests/unit/data` directory. See the contributing
  * guide in the manual for further details.
  */
 static Path getUnitTestData() {
diff --git a/src/libutil/tests/chunked-vector.cc b/tests/unit/libutil/tests/chunked-vector.cc
similarity index 100%
rename from src/libutil/tests/chunked-vector.cc
rename to tests/unit/libutil/tests/chunked-vector.cc
diff --git a/src/libutil/tests/closure.cc b/tests/unit/libutil/tests/closure.cc
similarity index 100%
rename from src/libutil/tests/closure.cc
rename to tests/unit/libutil/tests/closure.cc
diff --git a/src/libutil/tests/compression.cc b/tests/unit/libutil/tests/compression.cc
similarity index 100%
rename from src/libutil/tests/compression.cc
rename to tests/unit/libutil/tests/compression.cc
diff --git a/src/libutil/tests/config.cc b/tests/unit/libutil/tests/config.cc
similarity index 100%
rename from src/libutil/tests/config.cc
rename to tests/unit/libutil/tests/config.cc
diff --git a/src/libutil/tests/git.cc b/tests/unit/libutil/tests/git.cc
similarity index 99%
rename from src/libutil/tests/git.cc
rename to tests/unit/libutil/tests/git.cc
index 2842ea4d03f5..8aeb994e2591 100644
--- a/src/libutil/tests/git.cc
+++ b/tests/unit/libutil/tests/git.cc
@@ -87,7 +87,7 @@ TEST_F(GitTest, blob_write) {
 /**
  * This data is for "shallow" tree tests. However, we use "real" hashes
  * so that we can check our test data in the corresponding functional
- * test (`git-hashing/unit-test-data`).
+ * test (`git-hashing/tests/unit/data`).
  */
 const static Tree tree = {
     {
diff --git a/src/libutil/tests/hash.cc b/tests/unit/libutil/tests/hash.cc
similarity index 99%
rename from src/libutil/tests/hash.cc
rename to tests/unit/libutil/tests/hash.cc
index 9a5ebbb30fdc..813aaf1f186e 100644
--- a/src/libutil/tests/hash.cc
+++ b/tests/unit/libutil/tests/hash.cc
@@ -4,7 +4,7 @@
 #include <gtest/gtest.h>
 #include <rapidcheck/gtest.h>
 
-#include <hash.hh>
+#include "hash.hh"
 
 #include "tests/hash.hh"
 
diff --git a/src/libutil/tests/hash.hh b/tests/unit/libutil/tests/hash.hh
similarity index 100%
rename from src/libutil/tests/hash.hh
rename to tests/unit/libutil/tests/hash.hh
diff --git a/src/libutil/tests/hilite.cc b/tests/unit/libutil/tests/hilite.cc
similarity index 100%
rename from src/libutil/tests/hilite.cc
rename to tests/unit/libutil/tests/hilite.cc
diff --git a/src/libutil/tests/logging.cc b/tests/unit/libutil/tests/logging.cc
similarity index 100%
rename from src/libutil/tests/logging.cc
rename to tests/unit/libutil/tests/logging.cc
diff --git a/src/libutil/tests/lru-cache.cc b/tests/unit/libutil/tests/lru-cache.cc
similarity index 100%
rename from src/libutil/tests/lru-cache.cc
rename to tests/unit/libutil/tests/lru-cache.cc
diff --git a/src/libutil/tests/pool.cc b/tests/unit/libutil/tests/pool.cc
similarity index 100%
rename from src/libutil/tests/pool.cc
rename to tests/unit/libutil/tests/pool.cc
diff --git a/src/libutil/tests/references.cc b/tests/unit/libutil/tests/references.cc
similarity index 100%
rename from src/libutil/tests/references.cc
rename to tests/unit/libutil/tests/references.cc
diff --git a/src/libutil/tests/suggestions.cc b/tests/unit/libutil/tests/suggestions.cc
similarity index 100%
rename from src/libutil/tests/suggestions.cc
rename to tests/unit/libutil/tests/suggestions.cc
diff --git a/src/libutil/tests/tests.cc b/tests/unit/libutil/tests/tests.cc
similarity index 100%
rename from src/libutil/tests/tests.cc
rename to tests/unit/libutil/tests/tests.cc
diff --git a/src/libutil/tests/url.cc b/tests/unit/libutil/tests/url.cc
similarity index 100%
rename from src/libutil/tests/url.cc
rename to tests/unit/libutil/tests/url.cc
diff --git a/src/libutil/tests/xml-writer.cc b/tests/unit/libutil/tests/xml-writer.cc
similarity index 100%
rename from src/libutil/tests/xml-writer.cc
rename to tests/unit/libutil/tests/xml-writer.cc