assertEscaped() and assertUnescaped don't work as you would expect in JavascriptTestBase

This looks pretty good, but I would want to look at this when I get home on my dev machine so I can see the test run in place.

+++ b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
@@ -74,4 +74,30 @@ public function testError() {
+    $assert->assertNoEscaped('<p class="escaped">');

+++ b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
@@ -62,4 +69,30 @@ public function testCreateScreenshot() {
+    $assert->assertNoEscaped('<p class="escaped">');

+++ b/core/modules/system/tests/modules/test_page_test/src/Controller/Test.php
@@ -88,4 +89,30 @@ public function error() {
+      '#prefix' => '<div class="escaped">',

Looks like the assertions need to check for a div instead of a p element?

+++ b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
@@ -74,4 +74,30 @@ public function testError() {
+    $this->drupalGet('test-escaped-characters');
+    $assert->assertNoEscaped('<p class="escaped">');
...
+
+    $this->drupalGet('test-escaped-script');
+    $assert->assertNoEscaped('<p class="escaped">');

+++ b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
@@ -62,4 +69,34 @@ public function testCreateScreenshot() {
+
+    $this->drupalGet('test-escaped-characters');
+    $assert->assertNoEscaped('<div class="escaped">');
+    $assert->responseContains('<div class="escaped">');
...
+    $this->drupalGet('test-unescaped-script');
+    $assert->assertNoEscaped('<div class="unescaped">');
+    $assert->responseContains('<div class="unescaped">');

Don't we have the same problem over in BTBT as well?

I think this looks nice. Few questions / comments.

1. +++ b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
   @@ -79,4 +79,34 @@ public function testError() {
   +    $assert->assertEscaped('<');
   +    $assert->assertEscaped('\'');
   +    $assert->assertEscaped('"');
   +    $assert->assertEscaped('>');
   +    $assert->assertEscaped('&');
   +
   

   +++ b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
   @@ -62,4 +69,34 @@ public function testCreateScreenshot() {
   +    $assert->assertEscaped('<');
   +    $assert->assertEscaped('\'');
   +    $assert->assertEscaped('"');
   +    $assert->assertEscaped('>');
   +    $assert->assertEscaped('&');
   

   Would $assert->assertEscaped('Escaped: <"\'&>'); be a safer test in case those characters are in the response escaped, for whatever reason?

2. +++ b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
   @@ -28,4 +28,49 @@ public function assertWaitOnAjaxRequest($timeout = 10000, $message = 'Unable to
   +   * Drupal's Html::escape() uses the ENT_QUOTES flag with htmlspecialchars() to
   +   * escape both single and double quotes. With JavascriptTestBase testing the
   +   * browser is automatically converting " and ' to double and single
   +   * quotes respectively therefore we can not escape them them when testing for
   +   * escaped HTML.
   +   *
   

   I think we need a reference here. I cannot find anything about this behavior anywhere with Mink or PhantomJS.

#14 doesn't apply anymore.

Re-rolled.

Looks ready for prime time.

+++ b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
@@ -387,6 +387,51 @@ function t(r, lx, ly) {
+   * quotes respectively therefore we can not escape them them when testing for

Nit: them them (fixed on commit).

Committed 1d0a07f and pushed to 8.8.x. Thanks!

And cherry-picked to 8.7.x, thanks!