testing/synctest: fix inverted test failure message in TestContextAfterFunc

Fixes #75685

Change-Id: I5592becfde6aaca3d7f0e2f09bc7a9785228523e
GitHub-Last-Rev: 0ff7bd3
GitHub-Pull-Request: #75687
Reviewed-on: https://go-review.googlesource.com/c/go/+/708275
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Damien Neil <[email protected]>
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Reviewed-by: Sean Liao <[email protected]>

Author: fgm

src/testing/synctest/example_test.go

@@ -66,7 +66,7 @@ func TestContextAfterFunc(t *testing.T) {
 		cancel()
 		synctest.Wait()
 		if !afterFuncCalled {
-			t.Fatalf("before context is canceled: AfterFunc not called")
+			t.Fatalf("after context is canceled: AfterFunc not called")
 		}
 	})
 }

src/testing/synctest/synctest.go

@@ -147,7 +147,7 @@
 //			cancel()
 //			synctest.Wait()
 //			if !afterFuncCalled {
-//				t.Fatalf("before context is canceled: AfterFunc not called")
+//				t.Fatalf("after context is canceled: AfterFunc not called")
 //			}
 //		})
 //	}