Revert "testing: add T.Context method"

This reverts commit 26827bc2fe4c80dc68b3793631d24975425c9467.

Fixes #18199

Change-Id: I42e292cb4e3d740a4fbb5d0380c6ee15ac742092
Reviewed-on: https://go-review.googlesource.com/34141
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

4 files changed, 33 insertions, 95 deletions

diff --git a/src/testing/benchmark.go b/src/testing/benchmark.go
index b1c6d2eff0..c033ce5fec 100644
--- a/src/testing/benchmark.go
+++ b/src/testing/benchmark.go
@@ -5,7 +5,6 @@
 package testing
 
 import (
-	"context"
 	"flag"
 	"fmt"
 	"internal/race"
@@ -128,9 +127,6 @@ func (b *B) nsPerOp() int64 {
 
 // runN runs a single benchmark for the specified number of iterations.
 func (b *B) runN(n int) {
-	b.ctx, b.cancel = context.WithCancel(b.parentContext())
-	defer b.cancel()
-
 	benchmarkLock.Lock()
 	defer benchmarkLock.Unlock()
 	// Try to get a comparable environment for each run
diff --git a/src/testing/sub_test.go b/src/testing/sub_test.go
index 563e8656c6..2a24aaacfd 100644
--- a/src/testing/sub_test.go
+++ b/src/testing/sub_test.go
@@ -6,7 +6,6 @@ package testing
 
 import (
 	"bytes"
-	"context"
 	"regexp"
 	"strings"
 	"sync/atomic"
@@ -278,33 +277,28 @@ func TestTRun(t *T) {
 		ok:     true,
 		maxPar: 4,
 		f: func(t *T) {
-			// t.Parallel doesn't work in the pseudo-T we start with:
-			// it leaks a goroutine.
-			// Call t.Run to get a real one.
-			t.Run("X", func(t *T) {
-				t.Parallel()
-				for i := 0; i < 12; i++ {
-					t.Run("a", func(t *T) {
-						t.Parallel()
-						time.Sleep(time.Nanosecond)
-						for i := 0; i < 12; i++ {
-							t.Run("b", func(t *T) {
-								time.Sleep(time.Nanosecond)
-								for i := 0; i < 12; i++ {
-									t.Run("c", func(t *T) {
-										t.Parallel()
-										time.Sleep(time.Nanosecond)
-										t.Run("d1", func(t *T) {})
-										t.Run("d2", func(t *T) {})
-										t.Run("d3", func(t *T) {})
-										t.Run("d4", func(t *T) {})
-									})
-								}
-							})
-						}
-					})
-				}
-			})
+			t.Parallel()
+			for i := 0; i < 12; i++ {
+				t.Run("a", func(t *T) {
+					t.Parallel()
+					time.Sleep(time.Nanosecond)
+					for i := 0; i < 12; i++ {
+						t.Run("b", func(t *T) {
+							time.Sleep(time.Nanosecond)
+							for i := 0; i < 12; i++ {
+								t.Run("c", func(t *T) {
+									t.Parallel()
+									time.Sleep(time.Nanosecond)
+									t.Run("d1", func(t *T) {})
+									t.Run("d2", func(t *T) {})
+									t.Run("d3", func(t *T) {})
+									t.Run("d4", func(t *T) {})
+								})
+							}
+						})
+					}
+				})
+			}
 		},
 	}, {
 		desc:   "skip output",
@@ -347,7 +341,6 @@ func TestTRun(t *T) {
 			},
 			context: ctx,
 		}
-		root.ctx, root.cancel = context.WithCancel(context.Background())
 		ok := root.Run(tc.desc, tc.f)
 		ctx.release()
 
diff --git a/src/testing/testing.go b/src/testing/testing.go
index f08c5c6b8e..8fb6d8373e 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -204,7 +204,6 @@ package testing
 
 import (
 	"bytes"
-	"context"
 	"errors"
 	"flag"
 	"fmt"
@@ -262,14 +261,12 @@ type common struct {
 	mu         sync.RWMutex // guards output, failed, and done.
 	output     []byte       // Output generated by test or benchmark.
 	w          io.Writer    // For flushToParent.
-	ctx        context.Context
-	cancel     context.CancelFunc
-	chatty     bool // A copy of the chatty flag.
-	ran        bool // Test or benchmark (or one of its subtests) was executed.
-	failed     bool // Test or benchmark has failed.
-	skipped    bool // Test of benchmark has been skipped.
-	finished   bool // Test function has completed.
-	done       bool // Test is finished and all subtests have completed.
+	chatty     bool         // A copy of the chatty flag.
+	ran        bool         // Test or benchmark (or one of its subtests) was executed.
+	failed     bool         // Test or benchmark has failed.
+	skipped    bool         // Test of benchmark has been skipped.
+	finished   bool         // Test function has completed.
+	done       bool         // Test is finished and all subtests have completed.
 	hasSub     bool
 	raceErrors int // number of races detected during test
 
@@ -283,13 +280,6 @@ type common struct {
 	sub      []*T      // Queue of subtests to be run in parallel.
 }
 
-func (c *common) parentContext() context.Context {
-	if c == nil || c.parent == nil || c.parent.ctx == nil {
-		return context.Background()
-	}
-	return c.parent.ctx
-}
-
 // Short reports whether the -test.short flag is set.
 func Short() bool {
 	return *short
@@ -386,7 +376,6 @@ func fmtDuration(d time.Duration) string {
 
 // TB is the interface common to T and B.
 type TB interface {
-	Context() context.Context
 	Error(args ...interface{})
 	Errorf(format string, args ...interface{})
 	Fail()
@@ -434,15 +423,6 @@ func (c *common) Name() string {
 	return c.name
 }
 
-// Context returns the context for the current test or benchmark.
-// The context is cancelled when the test or benchmark finishes.
-// A goroutine started during a test or benchmark can wait for the
-// context's Done channel to become readable as a signal that the
-// test or benchmark is over, so that the goroutine can exit.
-func (c *common) Context() context.Context {
-	return c.ctx
-}
-
 func (c *common) setRan() {
 	if c.parent != nil {
 		c.parent.setRan()
@@ -619,9 +599,6 @@ type InternalTest struct {
 }
 
 func tRunner(t *T, fn func(t *T)) {
-	t.ctx, t.cancel = context.WithCancel(t.parentContext())
-	defer t.cancel()
-
 	// When this goroutine is done, either because fn(t)
 	// returned normally or because a test failure triggered
 	// a call to runtime.Goexit, record the duration and send
diff --git a/src/testing/testing_test.go b/src/testing/testing_test.go
index 9954f9af8c..45e44683b4 100644
--- a/src/testing/testing_test.go
+++ b/src/testing/testing_test.go
@@ -5,42 +5,14 @@
 package testing_test
 
 import (
-	"fmt"
 	"os"
-	"runtime"
 	"testing"
-	"time"
 )
 
-func TestMain(m *testing.M) {
-	g0 := runtime.NumGoroutine()
-
-	code := m.Run()
-	if code != 0 {
-		os.Exit(code)
-	}
+// This is exactly what a test would do without a TestMain.
+// It's here only so that there is at least one package in the
+// standard library with a TestMain, so that code is executed.
 
-	// Check that there are no goroutines left behind.
-	t0 := time.Now()
-	stacks := make([]byte, 1<<20)
-	for {
-		g1 := runtime.NumGoroutine()
-		if g1 == g0 {
-			return
-		}
-		stacks = stacks[:runtime.Stack(stacks, true)]
-		time.Sleep(50 * time.Millisecond)
-		if time.Since(t0) > 2*time.Second {
-			fmt.Fprintf(os.Stderr, "Unexpected leftover goroutines detected: %v -> %v\n%s\n", g0, g1, stacks)
-			os.Exit(1)
-		}
-	}
-}
-
-func TestContextCancel(t *testing.T) {
-	ctx := t.Context()
-	// Tests we don't leak this goroutine:
-	go func() {
-		<-ctx.Done()
-	}()
+func TestMain(m *testing.M) {
+	os.Exit(m.Run())
 }