cmd/internal/test2json: generate and validate test artifacts

Adds a mechanism for generating test2json test artifacts from and validating them against a real test. If a .test file has a corresponding .src file, TestGolden will now treat the .src file as a script test, executing it and verifying that the output matches the contents of the .test file. Running TestGolden with the -update flag will also regenerate .test files if they have a corresponding .src file.

Capturing the output of the script test in this way required making minor changes to cmd/internal/script/scripttest.

This was motivated by CL 601535 (golang/go#62728). Specifically, testing that CL required adding src/cmd/internal/test2json/testdata/frameescape.test which has a multitude of non-printing characters and thus must be generated by executing `go test`. Using a script test to generate the test file is more reliable than doing it by hand.

Change-Id: I60456700e37e21a42d0514be2ce86dc6df2bccb0
Reviewed-on: https://go-review.googlesource.com/c/go/+/628615
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/cmd/internal/script/scripttest/scripttest.go b/src/cmd/internal/script/scripttest/scripttest.go
index 349201fd18..418b063b28 100644
--- a/src/cmd/internal/script/scripttest/scripttest.go
+++ b/src/cmd/internal/script/scripttest/scripttest.go
@@ -89,7 +89,7 @@ func Run(t testing.TB, e *script.Engine, s *script.State, filename string, testS
 		return e.Execute(s, filename, bufio.NewReader(testScript), log)
 	}()
 
-	if skip, ok := errors.AsType[skipError](err); ok {
+	if skip, ok := errors.AsType[SkipError](err); ok {
 		if skip.msg == "" {
 			t.Skip("SKIP")
 		} else {
@@ -113,17 +113,18 @@ func Skip() script.Cmd {
 				return nil, script.ErrUsage
 			}
 			if len(args) == 0 {
-				return nil, skipError{""}
+				return nil, SkipError{""}
 			}
-			return nil, skipError{args[0]}
+			return nil, SkipError{args[0]}
 		})
 }
 
-type skipError struct {
+// SkipError is returned by a script test that executes the [Skip] command.
+type SkipError struct {
 	msg string
 }
 
-func (s skipError) Error() string {
+func (s SkipError) Error() string {
 	if s.msg == "" {
 		return "skip"
 	}