test(functional): add tests for new environment operation flags

Refs: #10795

maintainers/flake-module.nix

@@ -552,7 +552,6 @@
             ''^tests/functional/flakes/check\.sh$''
             ''^tests/functional/flakes/common\.sh$''
             ''^tests/functional/flakes/config\.sh$''
-            ''^tests/functional/flakes/develop\.sh$''
             ''^tests/functional/flakes/flakes\.sh$''
             ''^tests/functional/flakes/follow-paths\.sh$''
             ''^tests/functional/flakes/prefetch\.sh$''

tests/functional/flakes/develop.sh

@@ -5,11 +5,11 @@ source ../common.sh
 TODO_NixOS
 
 clearStore
-rm -rf $TEST_HOME/.cache $TEST_HOME/.config $TEST_HOME/.local
+rm -rf "$TEST_HOME/.cache" "$TEST_HOME/.config" "$TEST_HOME/.local"
 
 # Create flake under test.
-cp ../shell-hello.nix ../config.nix $TEST_HOME/
-cat <<EOF >$TEST_HOME/flake.nix
+cp ../shell-hello.nix ../config.nix "$TEST_HOME/"
+cat <<EOF >"$TEST_HOME/flake.nix"
 {
     inputs.nixpkgs.url = "$TEST_HOME/nixpkgs";
     outputs = {self, nixpkgs}: {
@@ -24,17 +24,17 @@ cat <<EOF >$TEST_HOME/flake.nix
 EOF
 
 # Create fake nixpkgs flake.
-mkdir -p $TEST_HOME/nixpkgs
-cp ../config.nix ../shell.nix $TEST_HOME/nixpkgs
-cat <<EOF >$TEST_HOME/nixpkgs/flake.nix
+mkdir -p "$TEST_HOME/nixpkgs"
+cp ../config.nix ../shell.nix "$TEST_HOME/nixpkgs"
+cat <<EOF >"$TEST_HOME/nixpkgs/flake.nix"
 {
     outputs = {self}: {
       legacyPackages.$system.bashInteractive = (import ./shell.nix {}).bashInteractive;
     };
 }
 EOF
 
-cd $TEST_HOME
+cd "$TEST_HOME"
 
 # Test whether `nix develop` passes through environment variables.
 [[ "$(
@@ -50,6 +50,85 @@ echo "\$ENVVAR"
 EOF
 )" ]]
 
+# Test wether `--keep-env-var` keeps the environment variable.
+(
+  expect='BAR'
+  got="$(FOO='BAR' nix develop --ignore-env --keep-env-var FOO --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test wether `--set-env-var` sets the environment variable.
+(
+  expect='BAR'
+  got="$(nix develop --ignore-env --set-env-var FOO 'BAR' --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test wether multiple `--unset-env-var` and `--set-env-var` cancle out
+(
+  expect=''
+  got="$(nix develop --set-env-var FOO 'BAR' --unset-env-var FOO --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test that `--unset-env-var` unsets the variable, regardless of where in the command it is.
+(
+  expect=''
+  got="$(nix develop --set-env-var FOO 'BAR' --unset-env-var FOO --set-env-var FOO 'BLA' --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test that `--set-env-var` overwrites previously set variables.
+(
+  expect='BLA'
+  got="$(nix develop --set-env-var FOO 'BAR' --set-env-var FOO 'BLA' --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test that `--set-env-var` overwrites previously set variables.
+(
+  expect='BLA'
+  got="$(FOO='BAR' nix develop --set-env-var FOO 'BLA' --no-write-lock-file .#hello <<EOF
+echo "\$FOO"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Test that multiple `--set-env-var` work.
+(
+  expect='BARFOO'
+  got="$(nix develop --set-env-var FOO 'BAR' --set-env-var BAR 'FOO' --no-write-lock-file .#hello <<EOF | tr -d '\n'
+echo "\$FOO"
+echo "\$BAR"
+EOF
+)"
+  [[ "$got" == "$expect" ]]
+)
+
+# Check that we throw an error when `--keep-env-var` is used without `--ignore-env`.
+expectStderr 1 nix develop --keep-env-var FOO .#hello |
+  grepQuiet "error: --keep-env-var does not make sense without --ignore-env"
+
+# Check that we throw an error when `--unset-env-var` is used with `--ignore-env`.
+expectStderr 1 nix develop --ignore-env --unset-env-var FOO .#hello |
+  grepQuiet "error: --unset-env-var does not make sense with --ignore-env"
+
 # Determine the bashInteractive executable.
 nix build --no-write-lock-file './nixpkgs#bashInteractive' --out-link ./bash-interactive
 BASH_INTERACTIVE_EXECUTABLE="$PWD/bash-interactive/bin/bash"