testing: implement testing.Cleanup

Also reorder and regroup common's fields slightly to match upstream.

TODO: pull in more upstream tests once this package is goroutine-safe

src/testing/sub_test.go

@@ -0,0 +1,80 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testing
+
+import (
+	"reflect"
+)
+
+func TestCleanup(t *T) {
+	var cleanups []int
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { cleanups = append(cleanups, 1) })
+		t.Cleanup(func() { cleanups = append(cleanups, 2) })
+	})
+	if got, want := cleanups, []int{2, 1}; !reflect.DeepEqual(got, want) {
+		t.Errorf("unexpected cleanup record; got %v want %v", got, want)
+	}
+}
+
+func TestRunCleanup(t *T) {
+	outerCleanup := 0
+	innerCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { outerCleanup++ })
+		t.Run("x", func(t *T) {
+			t.Cleanup(func() { innerCleanup++ })
+		})
+	})
+	if innerCleanup != 1 {
+		t.Errorf("unexpected inner cleanup count; got %d want 1", innerCleanup)
+	}
+	if outerCleanup != 1 {
+		t.Errorf("unexpected outer cleanup count; got %d want 0", outerCleanup)
+	}
+}
+
+func TestCleanupParallelSubtests(t *T) {
+	ranCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() { ranCleanup++ })
+		t.Run("x", func(t *T) {
+			t.Parallel()
+			if ranCleanup > 0 {
+				t.Error("outer cleanup ran before parallel subtest")
+			}
+		})
+	})
+	if ranCleanup != 1 {
+		t.Errorf("unexpected cleanup count; got %d want 1", ranCleanup)
+	}
+}
+
+func TestNestedCleanup(t *T) {
+	ranCleanup := 0
+	t.Run("test", func(t *T) {
+		t.Cleanup(func() {
+			if ranCleanup != 2 {
+				t.Errorf("unexpected cleanup count in first cleanup: got %d want 2", ranCleanup)
+			}
+			ranCleanup++
+		})
+		t.Cleanup(func() {
+			if ranCleanup != 0 {
+				t.Errorf("unexpected cleanup count in second cleanup: got %d want 0", ranCleanup)
+			}
+			ranCleanup++
+			t.Cleanup(func() {
+				if ranCleanup != 1 {
+					t.Errorf("unexpected cleanup count in nested cleanup: got %d want 1", ranCleanup)
+				}
+				ranCleanup++
+			})
+		})
+	})
+	if ranCleanup != 3 {
+		t.Errorf("unexpected cleanup count: got %d want 3", ranCleanup)
+	}
+}