os/signal: remove some arbitrary timeouts in tests

This should fix the test flake found in
https://build.golang.org/log/48ffb18e85dda480b7a67e8305dd03ee8337f170.

For #58901.

Change-Id: I1fcdd713a78e6b7c81e38133ce5f42f7f448a1a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/541115
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

src/os/signal/example_unix_test.go

@@ -12,9 +12,10 @@ import (
 	"log"
 	"os"
 	"os/signal"
-	"time"
 )
 
+var neverReady = make(chan struct{}) // never closed
+
 // This example passes a context with a signal to tell a blocking function that
 // it should abandon its work after a signal is received.
 func ExampleNotifyContext() {
@@ -35,8 +36,8 @@ func ExampleNotifyContext() {
 	}
 
 	select {
-	case <-time.After(time.Second):
+	case <-neverReady:
-		fmt.Println("missed signal")
+		fmt.Println("ready")
 	case <-ctx.Done():
 		fmt.Println(ctx.Err()) // prints "context canceled"
 		stop()                 // stop receiving signal notifications as soon as possible.

src/os/signal/signal_test.go

@@ -797,14 +797,10 @@ func TestNotifyContextStop(t *testing.T) {
 	}
 
 	stop()
-	select {
+	<-c.Done()
-	case <-c.Done():
 	if got := c.Err(); got != context.Canceled {
 		t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
 	}
-	case <-time.After(time.Second):
-		t.Errorf("timed out waiting for context to be done after calling stop")
-	}
 }
 
 func TestNotifyContextCancelParent(t *testing.T) {
@@ -818,14 +814,10 @@ func TestNotifyContextCancelParent(t *testing.T) {
 	}
 
 	cancelParent()
-	select {
+	<-c.Done()
-	case <-c.Done():
 	if got := c.Err(); got != context.Canceled {
 		t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
 	}
-	case <-time.After(time.Second):
-		t.Errorf("timed out waiting for parent context to be canceled")
-	}
 }
 
 func TestNotifyContextPrematureCancelParent(t *testing.T) {
@@ -840,14 +832,10 @@ func TestNotifyContextPrematureCancelParent(t *testing.T) {
 		t.Errorf("c.String() = %q, want %q", got, want)
 	}
 
-	select {
+	<-c.Done()
-	case <-c.Done():
 	if got := c.Err(); got != context.Canceled {
 		t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
 	}
-	case <-time.After(time.Second):
-		t.Errorf("timed out waiting for parent context to be canceled")
-	}
 }
 
 func TestNotifyContextSimultaneousStop(t *testing.T) {
@@ -868,14 +856,10 @@ func TestNotifyContextSimultaneousStop(t *testing.T) {
 		}()
 	}
 	wg.Wait()
-	select {
+	<-c.Done()
-	case <-c.Done():
 	if got := c.Err(); got != context.Canceled {
 		t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
 	}
-	case <-time.After(time.Second):
-		t.Errorf("expected context to be canceled")
-	}
 }
 
 func TestNotifyContextStringer(t *testing.T) {
@@ -920,7 +904,6 @@ func TestSignalTrace(t *testing.T) {
 		if err := trace.Start(buf); err != nil {
 			t.Fatalf("[%d] failed to start tracing: %v", i, err)
 		}
-		time.After(1 * time.Microsecond)
 		trace.Stop()
 		size := buf.Len()
 		if size == 0 {