stacktrace_ext_test.go stomps on GOPATH, losing track of code needed for the test

[nim-nim]

$ echo $GOPATH
/home/test/zap/zap-1.7.1/_build:/usr/share/gocode

$ ls /usr/share/gocode/src/github.com/stretchr/testify/assert/
assertion_forward.go  assertions.go  doc.go  errors.go  forward_assertions.go  http_assertions.go

$ cd /home/test/zap/zap-1.7.1/_build/src/go.uber.org/zap

$ go test -compiler gc -ldflags ''
# go.uber.org/zap
error_test.go:29:2: cannot find package "github.com/pkg/errors" in any of:
        /usr/lib/golang/src/github.com/pkg/errors (from $GOROOT)
        /home/test/zap/zap-1.7.1/_build/src/github.com/pkg/errors (from $GOPATH)
        /usr/share/gocode/src/github.com/pkg/errors
FAIL    go.uber.org/zap [setup failed]
[test@localhost zap]$ go test -compiler gc -ldflags ''
invalid value "unknown" for flag -level: unrecognized level: "unknown"
Usage of test:
  -level value
        minimum enabled logging level
--- FAIL: TestStacktraceFiltersVendorZap (0.05s)
        Error Trace:    stacktrace_ext_test.go:112
                        stacktrace_ext_test.go:141
                        stacktrace_ext_test.go:114
        Error:          Received unexpected error exit status 1
        Messages:       Failed to run test in vendor directory, output: # go.uber.org/zap_test
                stacktrace_ext_test.go:36:2: cannot find package "github.com/stretchr/testify/assert" in any of:
                        /tmp/gopath148698364/src/go.uber.org/zap_test/vendor/github.com/stretchr/testify/assert (vendor tree)
                        /usr/lib/golang/src/github.com/stretchr/testify/assert (from $GOROOT)
                        /tmp/gopath148698364/src/github.com/stretchr/testify/assert (from $GOPATH)
                FAIL    go.uber.org/zap_test [setup failed]


FAIL
exit status 1
FAIL    go.uber.org/zap 0.224s

[nim-nim]

stacktrace_ext_test.go:87: // We need to simulate a zap as a vendor library, so we're going to create a fake GOPATH

[prashantv]

To run zap tests, you need to install the Glide dependencies. This is done by running make dependencies as documented in the CONTRIBUTING doc:
https://github.com/uber-go/zap/blob/master/CONTRIBUTING.md

Tests are passing on Travis without any issue, and I've verified this locally. If I move my vendor directory, I'm able to reproduce the issue above, so running make dependencies should fix your issue.