From 259d39cbadd342fe22451a616cf06ef6a62498e7 Mon Sep 17 00:00:00 2001
From: Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
Date: Tue, 18 Mar 2025 17:40:05 +0100
Subject: [PATCH] UI/Headless: Wait for "reftest-wait" class removal before
 screenshotting

Resolves https://github.com/LadybirdBrowser/ladybird/issues/3984
---
 UI/Headless/Test.cpp | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/UI/Headless/Test.cpp b/UI/Headless/Test.cpp
index 347f2fdc0f2..e66d3176db6 100644
--- a/UI/Headless/Test.cpp
+++ b/UI/Headless/Test.cpp
@@ -286,6 +286,27 @@ void run_dump_test(HeadlessWebView& view, Test& test, URL::URL const& url, int t
     timer->start();
 }
 
+static String wait_for_reftest_completion = R"(
+function hasReftestWaitClass() {
+    return document.documentElement.classList.contains('reftest-wait');
+}
+
+if (!hasReftestWaitClass()) {
+    internals.signalTestIsDone("PASS");
+} else {
+    const observer = new MutationObserver(() => {
+        if (!hasReftestWaitClass()) {
+            internals.signalTestIsDone("PASS");
+        }
+    });
+
+    observer.observe(document.documentElement, {
+        attributes: true,
+        attributeFilter: ['class'],
+    });
+}
+)"_string;
+
 static void run_ref_test(HeadlessWebView& view, Test& test, URL::URL const& url, int timeout_in_milliseconds)
 {
     auto timer = Core::Timer::create_single_shot(timeout_in_milliseconds, [&view, &test]() {
@@ -343,7 +364,11 @@ static void run_ref_test(HeadlessWebView& view, Test& test, URL::URL const& url,
         view.on_test_complete({ test, TestResult::Crashed });
     };
 
-    view.on_load_finish = [&view, &test, on_test_complete = move(on_test_complete)](auto const&) {
+    view.on_load_finish = [&view](auto const&) {
+        view.run_javascript(wait_for_reftest_completion);
+    };
+
+    view.on_test_finish = [&view, &test, on_test_complete = move(on_test_complete)](auto const&) {
         if (test.actual_screenshot) {
             if (view.url().query().has_value() && view.url().query()->equals_ignoring_ascii_case("mismatch"sv)) {
                 test.ref_test_expectation_type = RefTestExpectationType::Mismatch;
@@ -364,10 +389,6 @@ static void run_ref_test(HeadlessWebView& view, Test& test, URL::URL const& url,
         }
     };
 
-    view.on_test_finish = [&](auto const&) {
-        dbgln("Unexpected text test finished during ref test for {}", url);
-    };
-
     view.on_set_test_timeout = [timer, timeout_in_milliseconds](double milliseconds) {
         if (milliseconds <= timeout_in_milliseconds)
             return;