testing: removed flakey test

The synchronization in this test is a bit complicated and likely
incorrect, judging from the sporadically hanging trybots.
Most of what this is supposed to test is already tested in
TestTestContext, so I'll just remove it.

Fixes #15170

Change-Id: If54db977503caa109cec4516974eda9191051888
Reviewed-on: https://go-review.googlesource.com/22080
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/testing/sub_test.go

@@ -226,57 +226,6 @@ func TestTRun(t *T) {
 				t.Errorf("count was %d; want 4", count)
 			}
 		},
-	}, {
-		desc:   "run no more than *parallel tests concurrently",
-		ok:     true,
-		maxPar: 4,
-		f: func(t *T) {
-			max := 0
-			in := make(chan int)
-			out := make(chan int)
-			ctx := t.context
-			t.Run("wait", func(t *T) {
-				t.Run("controller", func(t *T) {
-					// Verify sequential tests don't skew counts.
-					t.Run("seq1", func(t *T) {})
-					t.Run("seq2", func(t *T) {})
-					t.Run("seq3", func(t *T) {})
-					t.Parallel()
-					for i := 0; i < 80; i++ {
-						ctx.mu.Lock()
-						if ctx.running > max {
-							max = ctx.running
-						}
-						ctx.mu.Unlock()
-						<-in
-						// force a minimum to avoid a race, although it works
-						// without it.
-						if i >= ctx.maxParallel-2 { // max - this - 1
-							out <- i
-						}
-					}
-					close(out)
-				})
-				// Ensure we don't exceed the maximum even with nested parallelism.
-				for i := 0; i < 2; i++ {
-					t.Run("", func(t *T) {
-						t.Parallel()
-						for j := 0; j < 40; j++ {
-							t.Run("", func(t *T) {
-								t.Run("seq1", func(t *T) {})
-								t.Run("seq2", func(t *T) {})
-								t.Parallel()
-								in <- j
-								<-out
-							})
-						}
-					})
-				}
-			})
-			if max != ctx.maxParallel {
-				realTest.Errorf("max: got %d; want: %d", max, ctx.maxParallel)
-			}
-		},
 	}, {
 		desc: "alternate sequential and parallel",
 		// Sequential tests should partake in the counting of running threads.