diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index f0c5257..e5f833f 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -2514,7 +2514,7 @@ protected function clickLink($label, $index = 0) {
       $url_target = $this->getAbsoluteUrl($urls[$index]['href']);
     }
 
-    $this->assertTrue(isset($urls[$index]), String::format('Clicked link %label (@url_target) from @url_before', array('%label' => $label, '@url_target' => $url_target, '@url_before' => $url_before)), 'Browser');
+    $this->assertTrue(isset($urls[$index]), String::format('Clicked link %label (@url_target) from @url_before', array('%label' => $label, '@url_target' => isset($url_target) ? $url_target : '<none>', '@url_before' => $url_before)), 'Browser');
 
     if (isset($url_target)) {
       return $this->drupalGet($url_target);
diff --git a/core/modules/simpletest/tests/src/WebTestBaseTest.php b/core/modules/simpletest/tests/src/WebTestBaseTest.php
index 8bce846..b8ac5d3 100644
--- a/core/modules/simpletest/tests/src/WebTestBaseTest.php
+++ b/core/modules/simpletest/tests/src/WebTestBaseTest.php
@@ -86,4 +86,106 @@ public function testAssertFieldByName($filename, $name, $value, $expected) {
     $test_method->invokeArgs($web_test, array($name, $value, 'message'));
   }
 
+  /**
+   * Data provider for testClickLink().
+   *
+   * @return array
+   *   Array of arrays of test data. Test data is structured as follows:
+   *   - Expected return value of clickLink().
+   *   - Parameter $label to clickLink().
+   *   - Parameter $index to clickLink().
+   *   - Test data to be returned by mocked xpath(). Return an empty array here
+   *     to mock no link found on the page.
+   */
+  public function providerTestClickLink() {
+    return array(
+      // Test for a non-existent label.
+      array(
+        FALSE,
+        'does_not_exist',
+        0,
+        array(),
+      ),
+      // Test for an existing label.
+      array(
+        'This Text Returned By drupalGet()',
+        'exists',
+        0,
+        array(0 => array('href' => 'this_is_a_url')),
+      ),
+      // Test for an existing label that isn't the first one.
+      array(
+        'This Text Returned By drupalGet()',
+        'exists',
+        1,
+        array(
+          0 => array('href' => 'this_is_a_url'),
+          1 => array('href' => 'this_is_another_url'),
+        ),
+      ),
+    );
+  }
+
+  /**
+   * Test WebTestBase::clickLink().
+   *
+   * @dataProvider providerTestClickLink
+   *
+   * @param mixed $expected
+   *   Expected return value of clickLink().
+   * @param string $label
+   *   Parameter $label to clickLink().
+   * @param int $index
+   *   Parameter $index to clickLink().
+   * @param array $xpath_data
+   *   Test data to be returned by mocked xpath().
+   */
+  public function testClickLink($expected, $label, $index, $xpath_data) {
+    // Mock a WebTestBase object and some of its methods.
+    $web_test = $this->getMockBuilder('Drupal\simpletest\WebTestBase')
+      ->disableOriginalConstructor()
+      ->setMethods(array(
+        'assertTrue',
+        'getUrl',
+        'xpath',
+        'drupalGet',
+        'getAbsoluteUrl',
+      ))
+      ->getMock();
+
+    // Mocked getUrl() is only used for reporting so we just return a string.
+    $web_test->expects($this->any())
+      ->method('getUrl')
+      ->will($this->returnValue('url_before'));
+
+    // Mocked xpath() should return our test data.
+    $web_test->expects($this->any())
+      ->method('xpath')
+      ->will($this->returnValue($xpath_data));
+
+    // Mocked getAbsoluteUrl() should return whatever comes in.
+    $web_test->expects($this->any())
+      ->method('getAbsoluteUrl')
+      ->will($this->returnArgument(0));
+
+    // Mocked assertTrue() does nothing.
+    $web_test->expects($this->any())
+      ->method('assertTrue')
+      ->will($this->returnValue(NULL));
+
+    // We're only testing clickLink(), so drupalGet() always returns a string.
+    $web_test->expects($this->any())
+      ->method('drupalGet')
+      ->will($this->returnValue('This Text Returned By drupalGet()'));
+
+    // Set the clickLink() method to public so we can test it.
+    $clicklink_method = new \ReflectionMethod($web_test, 'clickLink');
+    $clicklink_method->setAccessible(TRUE);
+
+    // The test itself.
+    $this->assertSame(
+      $expected, $clicklink_method->invoke($web_test, $label, $index), 'clickLink() valid.'
+    );
+  }
+
 }