cmd/go: ignore irrelevant 'go test' failure in TestGoTestRaceInstallCgo

This test runs 'go test -race -i runtime/race' and checks that it did
not overwrite cmd/cgo.

If GOROOT/pkg is read-only and GOROOT/pkg/$GOOS_$GOARCH_race is not
already populated, as are the conditions if the Go toolchain was
installed from source as root using 'make.bash', then 'go test -race
-i' itself will fail because it cannot install packages to GOROOT/pkg.

However, such a failure is not relevant to the test: even if 'go test
-race -i' fails, we can still verify that it did not incidentally
overwrite cmd/cgo.

Updates #28387
Updates #30316

Change-Id: Iff2f75a0aeb4c926290ac3062c83695604522078
Reviewed-on: https://go-review.googlesource.com/c/go/+/207959
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/go_test.go

@@ -3308,7 +3308,17 @@ func TestGoTestRaceInstallCgo(t *testing.T) {
 	cgo := strings.TrimSpace(tg.stdout.String())
 	old, err := os.Stat(cgo)
 	tg.must(err)
-	tg.run("test", "-race", "-i", "runtime/race")
+
+	// For this test, we don't actually care whether 'go test -race -i' succeeds.
+	// It may fail, for example, if GOROOT was installed from source as root and
+	// is now read-only.
+	// We only care that — regardless of whether it succeeds — it does not
+	// overwrite cmd/cgo.
+	runArgs := []string{"test", "-race", "-i", "runtime/race"}
+	if status := tg.doRun(runArgs); status != nil {
+		tg.t.Logf("go %v failure ignored: %v", runArgs, status)
+	}
+
 	new, err := os.Stat(cgo)
 	tg.must(err)
 	if !new.ModTime().Equal(old.ModTime()) {