net/http: deflake TestClientTimeout

Should fix flakes like:

https://build.golang.org/log/c8da331317064227f38d5ef57ed7dba563ba1b38

--- FAIL: TestClientTimeout_h1 (0.35s)
    client_test.go:1263: timeout after 200ms waiting for timeout of 100ms
FAIL

Change-Id: I0a4dba607524e8d7a00f498e27d9598acde5d222
Reviewed-on: https://go-review.googlesource.com/33420
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/client_test.go

@@ -1188,9 +1188,7 @@ func TestClientTimeout_h2(t *testing.T) { testClientTimeout(t, h2Mode) }
 func testClientTimeout(t *testing.T, h2 bool) {
 	setParallel(t)
 	defer afterTest(t)
-	testDone := make(chan struct{})
+	testDone := make(chan struct{}) // closed in defer below
-
-	const timeout = 100 * time.Millisecond
 
 	sawRoot := make(chan bool, 1)
 	sawSlow := make(chan bool, 1)
@@ -1204,21 +1202,22 @@ func testClientTimeout(t *testing.T, h2 bool) {
 			sawSlow <- true
 			w.Write([]byte("Hello"))
 			w.(Flusher).Flush()
-			select {
+			<-testDone
-			case <-testDone:
-			case <-time.After(timeout * 10):
-			}
 			return
 		}
 	}))
 	defer cst.close()
-	defer close(testDone)
+	defer close(testDone) // before cst.close, to unblock /slow handler
+
+	// 200ms should be long enough to get a normal request (the /
+	// handler), but not so long that it makes the test slow.
+	const timeout = 200 * time.Millisecond
 	cst.c.Timeout = timeout
 
 	res, err := cst.c.Get(cst.ts.URL)
 	if err != nil {
 		if strings.Contains(err.Error(), "Client.Timeout") {
-			t.Skip("host too slow to get fast resource in 100ms")
+			t.Skipf("host too slow to get fast resource in %v", timeout)
 		}
 		t.Fatal(err)
 	}
@@ -1244,7 +1243,7 @@ func testClientTimeout(t *testing.T, h2 bool) {
 		res.Body.Close()
 	}()
 
-	const failTime = timeout * 2
+	const failTime = 5 * time.Second
 	select {
 	case err := <-errc:
 		if err == nil {