diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index b4776d5..f8d6ae8 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -317,6 +317,7 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
   // this variable.
   if ($base_url) {
     putenv('SIMPLETEST_BASE_URL=' . $base_url);
+    putenv('BROWSERTEST_OUTPUT_DIRECTORY=' . \Drupal::service('file_system')->realpath('public://simpletest'));
   }
   $phpunit_bin = simpletest_phpunit_command();
 
@@ -324,6 +325,8 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
     $phpunit_bin,
     '--log-junit',
     escapeshellarg($phpunit_file),
+    '--printer',
+    '\\\Drupal\\\Tests\\\Listeners\\\SimpletestUiPrinter',
   );
 
   // Optimized for running a single test.
@@ -357,6 +360,7 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
   putenv('SIMPLETEST_DB=');
   if ($base_url) {
     putenv('SIMPLETEST_BASE_URL=');
+    putenv('BROWSERTEST_OUTPUT_DIRECTORY=');
   }
   return $ret;
 }
diff --git a/core/modules/simpletest/src/Tests/UiPhpUnitOutputTest.php b/core/modules/simpletest/src/Tests/UiPhpUnitOutputTest.php
new file mode 100644
index 0000000..324bf1d
--- /dev/null
+++ b/core/modules/simpletest/src/Tests/UiPhpUnitOutputTest.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\simpletest\Tests;
+
+use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\simpletest\Functional\SimpletestPhpunitBrowserTest;
+
+/**
+ * Test PHPUnit output for the Simpletest UI.
+ *
+ * @group simpletest
+ *
+ * @see \Drupal\Tests\Listeners\SimpletestUiPrinter
+ */
+class UiPhpUnitOutputTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var string[]
+   */
+  public static $modules = ['simpletest'];
+
+  /**
+   * Tests that PHPUnit output in the Simpletest UI looks good.
+   */
+  public function testOutput() {
+    require_once __DIR__ . '/../../tests/fixtures/simpletest_phpunit_browsertest.php';
+    $phpunit_junit_file = $this->container->get('file_system')->realpath('public://phpunit_junit.xml');
+    // Prepare the default browser test output directory in the child site.
+    $this->container->get('file_system')->mkdir('public://simpletest');
+    $status = 0;
+    $output = [];
+    simpletest_phpunit_run_command([SimpletestPhpunitBrowserTest::class], $phpunit_junit_file, $status, $output);
+
+    // Check that there are <br> tags for the HTML output by
+    // SimpletestUiPrinter.
+    $this->assertEqual($output[18], 'HTML output was generated<br />');
+    // Check that URLs are printed as HTML links.
+    $this->assertIdentical(strpos($output[19], '<a href="http'), 0);
+  }
+
+}
diff --git a/core/modules/simpletest/tests/fixtures/simpletest_phpunit_browsertest.php b/core/modules/simpletest/tests/fixtures/simpletest_phpunit_browsertest.php
new file mode 100644
index 0000000..0e9c416
--- /dev/null
+++ b/core/modules/simpletest/tests/fixtures/simpletest_phpunit_browsertest.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Drupal\Tests\simpletest\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * A PHPUnit-based browser test that will be run from Simpletest.
+ *
+ * To avoid accidentally running it is not in a normal PSR-4 directory.
+ *
+ * @group simpletest
+ */
+class SimpletestPhpunitBrowserTest extends BrowserTestBase {
+
+  /**
+   * Dummy test that logs the visited front page for HTML output.
+   */
+  public function testOutput() {
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseContains('<h2>TEST escaping</h2>');
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php b/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php
new file mode 100644
index 0000000..bfb91d7
--- /dev/null
+++ b/core/tests/Drupal/Tests/Listeners/SimpletestUiPrinter.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Drupal\Tests\Listeners;
+
+use Drupal\Component\Utility\Html;
+
+/**
+ * Defines a class for providing html output links in the Simpletest UI.
+ */
+class SimpletestUiPrinter extends HtmlOutputPrinter {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function write($buffer) {
+    $buffer = Html::escape($buffer);
+    // Turn HTML output URLs into clickable link <a> tags.
+    $url_pattern = '@https?://[^\s]+@';
+    $buffer = preg_replace($url_pattern, '<a href="$0" target="_blank" title="$0">$0</a>', $buffer);
+    // Make the output readable in HTML by breaking up lines properly.
+    $buffer = nl2br($buffer);
+
+    print $buffer;
+  }
+
+}