testing: add Context

Adds a new Context method to testing.T, that returns a context, that is
canceled before the end of its test function.

Fixes #36532.

Change-Id: I9315ad4dad25529d0b5be809e2d9db4e7528b5f2
GitHub-Last-Rev: 1c3fd6c4d8a9cc68a61f2df284d04d3d080216be
GitHub-Pull-Request: golang/go#68828
Reviewed-on: https://go-review.googlesource.com/c/go/+/603959
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/src/testing/testing_test.go b/src/testing/testing_test.go
index af6035fd27..ff674fc3d1 100644
--- a/src/testing/testing_test.go
+++ b/src/testing/testing_test.go
@@ -6,6 +6,8 @@ package testing_test
 
 import (
 	"bytes"
+	"context"
+	"errors"
 	"fmt"
 	"internal/race"
 	"internal/testenv"
@@ -918,3 +920,29 @@ func TestParentRun(t1 *testing.T) {
 		})
 	})
 }
+
+func TestContext(t *testing.T) {
+	ctx := t.Context()
+	if err := ctx.Err(); err != nil {
+		t.Fatalf("expected non-canceled context, got %v", err)
+	}
+
+	var innerCtx context.Context
+	t.Run("inner", func(t *testing.T) {
+		innerCtx = t.Context()
+		if err := innerCtx.Err(); err != nil {
+			t.Fatalf("expected inner test to not inherit canceled context, got %v", err)
+		}
+	})
+	t.Run("inner2", func(t *testing.T) {
+		if !errors.Is(innerCtx.Err(), context.Canceled) {
+			t.Fatal("expected context of sibling test to be canceled after its test function finished")
+		}
+	})
+
+	t.Cleanup(func() {
+		if !errors.Is(ctx.Err(), context.Canceled) {
+			t.Fatal("expected context canceled before cleanup")
+		}
+	})
+}