diff --git a/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
index c277e79..dafe8e3 100644
--- a/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
+++ b/core/modules/simpletest/tests/src/FunctionalJavascript/BrowserWithJavascriptTest.php
@@ -32,8 +32,7 @@ public function testJavascript() {
         return x == 400 && y == 300;
     }());
 JS;
-    $result = $this->wait($javascript);
-    $this->assertTrue($result);
+    $this->assertJsCondition($javascript);
   }
 
 }
diff --git a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
index 616cb27..c2354a0 100644
--- a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
+++ b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
@@ -46,11 +46,11 @@ public function testToolbarToggling() {
     $this->assertElementNotPresent('#toolbar-item-administration-tray.toolbar-tray-vertical', 'Toolbar tray is not vertically oriented by default.');
 
     $this->click('#toolbar-item-administration-tray button.toolbar-icon-toggle-vertical');
-    $this->assertTrue($this->wait('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-vertical")'));
+    $this->assertJsCondition('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-vertical")');
     $this->assertElementVisible('#toolbar-item-administration-tray.toolbar-tray-vertical', 'After toggling the orientation the toolbar tray is now displayed vertically.');
 
     $this->click('#toolbar-item-administration-tray button.toolbar-icon-toggle-horizontal');
-    $this->assertTrue($this->wait('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-horizontal")'));
+    $this->assertJsCondition('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-horizontal")');
     $this->assertElementVisible('#toolbar-item-administration-tray.toolbar-tray-horizontal', 'After toggling the orientation a second time the toolbar tray is displayed horizontally again.');
   }
 
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index 906f23e..e2324c7 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -71,11 +71,12 @@ protected function assertElementNotVisible($css_selector, $message = '') {
    * @param int $timeout
    *   (Optional) Timeout in milliseconds, defaults to 1000.
    *
-   * @return bool
-   *   The result of the JS condition.
+   * @throws \PHPUnit_Framework_AssertionFailedError
    */
-  protected function wait($condition, $timeout = 1000) {
-    return $this->getSession()->getDriver()->wait($timeout, $condition);
+  protected function assertJsCondition($condition, $timeout = 1000, $message = '') {
+    $message = $message ?: "Javascript condition met:\n" . $condition;
+    $result = $this->getSession()->getDriver()->wait($timeout, $condition);
+    $this->assertTrue($result, $message);
   }
 
 }