internal/vcs: avoid using os.Environ in a test helper

As reported by GODEBUG=gocachehash=1, this caused every single env var
set in the current environment to be part of the test cache key:

    $ grep testInput before | wc -l
    284
    $ grep testInput after | wc -l
    39

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I9e8f87bbe60fda9b3d37817a4c24c8ace24a9018
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1201442
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

internal/ci/checks/commit_test.go

@@ -38,9 +38,9 @@ func TestCommits(t *testing.T) {
 		t.Logf("commit:\n%s", commit)
 
 		dir := t.TempDir()
-		vcs.InitTestEnv(t)
-		mustRunCmd(t, dir, "git", "init")
-		mustRunCmd(t, dir, "git",
+		env := vcs.TestEnv()
+		mustRunCmd(t, dir, env, "git", "init")
+		mustRunCmd(t, dir, env, "git",
 			"-c", "[email protected]",
 			"-c", "user.name=cueckoo",
 			"commit", "--allow-empty", "-m", string(commit),
@@ -71,9 +71,10 @@ func TestCommits(t *testing.T) {
 	}
 }
 
-func mustRunCmd(t *testing.T, dir string, exe string, args ...string) {
+func mustRunCmd(t *testing.T, dir string, env []string, exe string, args ...string) {
 	cmd := exec.Command(exe, args...)
 	cmd.Dir = dir
+	cmd.Env = env
 	data, err := cmd.CombinedOutput()
 	qt.Assert(t, qt.IsNil(err), qt.Commentf("output: %q", data))
 }

internal/vcs/vcs.go

@@ -24,8 +24,6 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
-	"strings"
-	"testing"
 	"time"
 )
 
@@ -148,26 +146,20 @@ func homeEnvName() string {
 	}
 }
 
-// InitTestEnv sets up the environment so that any executed VCS command
+// TestEnv builds an environment so that any executed VCS command with it
 // won't be affected by the outer level environment.
 //
 // Note that this function is exposed so we can reuse it from other test packages
 // which also need to use Go tests with VCS systems.
 // Exposing a test helper is fine for now, given this is an internal package.
-func InitTestEnv(t testing.TB) {
-	t.Helper()
-	path := os.Getenv("PATH")
-	systemRoot := os.Getenv("SYSTEMROOT")
-	// First unset all environment variables to make a pristine environment.
-	for _, kv := range os.Environ() {
-		key, _, _ := strings.Cut(kv, "=")
-		t.Setenv(key, "")
-		os.Unsetenv(key)
+func TestEnv() []string {
+	env := []string{
+		"PATH=" + os.Getenv("PATH"),
+		homeEnvName() + "=/no-home",
 	}
-	os.Setenv("PATH", path)
-	os.Setenv(homeEnvName(), "/no-home")
 	// Must preserve SYSTEMROOT on Windows: https://github.com/golang/go/issues/25513 et al
 	if runtime.GOOS == "windows" {
-		os.Setenv("SYSTEMROOT", systemRoot)
+		env = append(env, "SYSTEMROOT="+os.Getenv("SYSTEMROOT"))
 	}
+	return env
 }

internal/vcs/vcs_test.go

@@ -51,8 +51,8 @@ func TestGit(t *testing.T) {
 	_, err = New("git", subdir)
 	qt.Assert(t, qt.ErrorMatches(err, `git VCS not found in any parent of ".+"`))
 
-	InitTestEnv(t)
-	mustRunCmd(t, dir, "git", "init")
+	env := TestEnv()
+	mustRunCmd(t, dir, env, "git", "init")
 	v, err := New("git", subdir)
 	qt.Assert(t, qt.IsNil(err))
 
@@ -63,13 +63,13 @@ func TestGit(t *testing.T) {
 	qt.Assert(t, qt.IsNil(err))
 	qt.Assert(t, qt.IsTrue(statusuncommitted.Uncommitted))
 
-	mustRunCmd(t, dir, "git", "add", ".")
+	mustRunCmd(t, dir, env, "git", "add", ".")
 	statusuncommitted, err = v.Status(ctx, subdir)
 	qt.Assert(t, qt.IsNil(err))
 	qt.Assert(t, qt.IsTrue(statusuncommitted.Uncommitted))
 
 	commitTime := time.Now().Truncate(time.Second)
-	mustRunCmd(t, dir, "git",
+	mustRunCmd(t, dir, env, "git",
 		"-c", "[email protected]",
 		"-c", "user.name=cueckoo",
 		"commit", "-m", "something",
@@ -186,9 +186,10 @@ func TestGit(t *testing.T) {
 	qt.Assert(t, qt.IsTrue(statusmissing.Uncommitted))
 }
 
-func mustRunCmd(t *testing.T, dir string, exe string, args ...string) {
+func mustRunCmd(t *testing.T, dir string, env []string, exe string, args ...string) {
 	c := exec.Command(exe, args...)
 	c.Dir = dir
+	c.Env = env
 	data, err := c.CombinedOutput()
 	qt.Assert(t, qt.IsNil(err), qt.Commentf("output: %q", data))
 }