Add a test for WaitForLoadState domcontentloaded

This test will ensure that when WaitForLoadState with waitUntil
domcontentloaded is called, that it doesn't block for the lifecycle
event if that event has already fired, and so using the frame's
internal state to unblock quickly.

Author: ankur22

tests/lifecycle_wait_test.go

@@ -68,6 +68,62 @@ func TestLifecycleWaitForLoadStateLoad(t *testing.T) {
 	})
 }
 
+func TestLifecycleWaitForLoadStateDOMContentLoaded(t *testing.T) {
+	// Test description
+	//
+	// 1. goto /home and wait for the domcontentloaded lifecycle event.
+	// 2. use WaitForLoadState with domcontentloaded to ensure that
+	//    domcontentloaded lifecycle event has already fired.
+	//
+	// Success criteria: We don't wait for all network requests or the
+	//                   async scripts to complete, and we're only
+	//                   interested in the html file being loaded. We
+	//                   also want to ensure that the domcontentloaded
+	//                   event is stored internally, and we don't block
+	//                   on WaitForLoadState.
+
+	t.Parallel()
+
+	tb := newTestBrowser(t, withFileServer())
+	p := tb.NewPage(nil)
+	tb.withHandler("/home", func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, tb.staticURL("wait_for_nav_lifecycle.html"), http.StatusMovedPermanently)
+	})
+
+	var counter int64
+	var counterMu sync.Mutex
+	tb.withHandler("/ping", func(w http.ResponseWriter, _ *http.Request) {
+		counterMu.Lock()
+		defer counterMu.Unlock()
+
+		time.Sleep(time.Millisecond * 100)
+
+		counter++
+		fmt.Fprintf(w, "pong %d", counter)
+	})
+
+	tb.withHandler("/ping.js", func(w http.ResponseWriter, _ *http.Request) {
+		fmt.Fprintf(w, `
+				await new Promise(resolve => setTimeout(resolve, 1000));
+
+				var pingJSTextOutput = document.getElementById("pingJSText");
+				pingJSTextOutput.innerText = "ping.js loaded from server";
+			`)
+	})
+
+	waitUntil := common.LifecycleEventDOMContentLoad
+	assertHome(t, tb, p, waitUntil, func() {
+		result := p.TextContent("#pingRequestText", nil)
+		assert.NotEqualValues(t, "Waiting... pong 10 - for loop complete", result)
+
+		result = p.TextContent("#pingJSText", nil)
+		assert.EqualValues(t, "Waiting...", result)
+
+		// This shouldn't block and return after calling hasLifecycleEventFired.
+		p.WaitForLoadState(waitUntil.String(), nil)
+	})
+}
+
 func TestLifecycleReloadLoad(t *testing.T) {
 	t.Parallel()