testing: failfast fails fast when Fatal called

When a test calls t.Fatal()/t.Fatalf(), only deferred code will execute.
Increment the failure count as part of a deferred call.

Fixes #24412

Change-Id: Ibb154015fcd3d0fb7739718fdda8c9ad22f9e896
Reviewed-on: https://go-review.googlesource.com/101035
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -5700,6 +5700,9 @@ func TestFailFast(t *testing.T) {
 		// non-parallel subtests:
 		{"TestFailingSubtestsA", true, 1},
 		{"TestFailingSubtestsA", false, 2},
+		// fatal test
+		{"TestFatal[CD]", true, 1},
+		{"TestFatal[CD]", false, 2},
 	}
 
 	for _, tt := range tests {

src/cmd/go/testdata/src/failfast_test.go

@@ -52,3 +52,11 @@ func TestFailingSubtestsA(t *testing.T) {
 func TestFailingB(t *testing.T) {
 	t.Errorf("FAIL - %s", t.Name())
 }
+
+func TestFatalC(t *testing.T) {
+	t.Fatalf("FAIL - %s", t.Name())
+}
+
+func TestFatalD(t *testing.T) {
+	t.Fatalf("FAIL - %s", t.Name())
+}

src/testing/testing.go

@@ -731,6 +731,10 @@ func tRunner(t *T, fn func(t *T)) {
 	// a call to runtime.Goexit, record the duration and send
 	// a signal saying that the test is done.
 	defer func() {
+		if t.failed {
+			atomic.AddUint32(&numFailed, 1)
+		}
+
 		if t.raceErrors+race.Errors() > 0 {
 			t.Errorf("race detected during execution of test")
 		}
@@ -790,9 +794,7 @@ func tRunner(t *T, fn func(t *T)) {
 	t.raceErrors = -race.Errors()
 	fn(t)
 
-	if t.failed {
+	// code beyond here will not be executed when FailNow is invoked
-		atomic.AddUint32(&numFailed, 1)
-	}
 	t.finished = true
 }