tests: extract submit-after-close in its own test

Signed-off-by: Alexandre Perrin <[email protected]>

workerpool_test.go

@@ -199,10 +199,6 @@ func TestWorkerPool(t *testing.T) {
 		t.Errorf("close: got '%v', want no error", err)
 	}
 
-	if err := wp.Submit("", nil); err != ErrClosed {
-		t.Errorf("submit: got '%v', want '%v'", err, ErrClosed)
-	}
-
 	results, err := wp.Drain()
 	if err != ErrClosed {
 		t.Errorf("drain: got '%v', want '%v'", err, ErrClosed)
@@ -283,6 +279,14 @@ func TestConcurrentDrain(t *testing.T) {
 	wg.Wait()
 }
 
+func TestWorkerPoolSubmitAfterClose(t *testing.T) {
+	wp := New(runtime.NumCPU())
+	wp.Close()
+	if err := wp.Submit("dummy", nil); err != ErrClosed {
+		t.Fatalf("got %v; want %v", err, ErrClosed)
+	}
+}
+
 func TestWorkerPoolManyClose(t *testing.T) {
 	wp := New(runtime.NumCPU())