testhelper: Use `t.Setenv()` to detect misuse with `t.Parallel()`

When using `os.Setenv()`, we change the environment variable for the
full process. While not surprising, this means that we must avoid this
in parallel tests given that the environment variable would also be set
for any other, currently running tests.

With Go v1.17 a new `t.Setenv()` helper function has been introduced
that detects this case and that instead causes us to panic. Convert
`testhelper.ModifyEnvironment()` to use that function and fix a test
that is using `t.Parallel()`.

2 files changed, 6 insertions, 11 deletions

diff --git a/internal/gitaly/service/repository/create_fork_test.go b/internal/gitaly/service/repository/create_fork_test.go
index b23b85bc3..53651c408 100644
--- a/internal/gitaly/service/repository/create_fork_test.go
+++ b/internal/gitaly/service/repository/create_fork_test.go
@@ -43,8 +43,6 @@ import (
 )
 
 func TestCreateFork_successful(t *testing.T) {
-	t.Parallel()
-
 	// We need to inject this once across all tests given that crypto/x509 only initializes
 	// certificates once. Changing injected certs during our tests is thus not going to fly well
 	// and would cause failure. We should eventually address this and provide better testing
diff --git a/internal/testhelper/testhelper.go b/internal/testhelper/testhelper.go
index db65feeb3..dacf805b3 100644
--- a/internal/testhelper/testhelper.go
+++ b/internal/testhelper/testhelper.go
@@ -274,17 +274,14 @@ func ModifyEnvironment(t testing.TB, key string, value string) {
 	oldValue, hasOldValue := os.LookupEnv(key)
 	if value == "" {
 		require.NoError(t, os.Unsetenv(key))
+		t.Cleanup(func() {
+			if hasOldValue {
+				require.NoError(t, os.Setenv(key, oldValue))
+			}
+		})
 	} else {
-		require.NoError(t, os.Setenv(key, value))
+		t.Setenv(key, value)
 	}
-
-	t.Cleanup(func() {
-		if hasOldValue {
-			require.NoError(t, os.Setenv(key, oldValue))
-		} else {
-			require.NoError(t, os.Unsetenv(key))
-		}
-	})
 }
 
 // GenerateCerts creates a certificate that can be used to establish TLS protected TCP connection.