diff --git a/core/modules/simpletest/src/TestDiscovery.php b/core/modules/simpletest/src/TestDiscovery.php
index a6c0e62..f3a0449 100644
--- a/core/modules/simpletest/src/TestDiscovery.php
+++ b/core/modules/simpletest/src/TestDiscovery.php
@@ -79,8 +79,9 @@ public function registerTestNamespaces() {
 
     $existing = $this->classLoader->getPrefixesPsr4();
 
-    // Add PHPUnit test namespace of Drupal core.
+    // Add PHPUnit test namespaces of Drupal core.
     $this->testNamespaces['Drupal\\Tests\\'] = [DRUPAL_ROOT . '/core/tests/Drupal/Tests'];
+    $this->testNamespaces['Drupal\\FunctionalTests\\'] = [DRUPAL_ROOT . '/core/tests/Drupal/FunctionalTests'];
 
     $this->availableExtensions = array();
     foreach ($this->getExtensions() as $name => $extension) {
@@ -95,8 +96,9 @@ public function registerTestNamespaces() {
       // Add Simpletest test namespace.
       $this->testNamespaces["Drupal\\$name\\Tests\\"][] = "$base_path/src/Tests";
 
-      // Add PHPUnit test namespace.
-      $this->testNamespaces["Drupal\\Tests\\$name\\"][] = "$base_path/tests/src";
+      // Add PHPUnit test namespaces.
+      $this->testNamespaces["Drupal\\Tests\\$name\\Unit\\"][] = "$base_path/tests/src/Unit";
+      $this->testNamespaces["Drupal\\Tests\\$name\\Functional\\"][] = "$base_path/tests/src/Functional";
     }
 
     foreach ($this->testNamespaces as $prefix => $paths) {
@@ -322,7 +324,7 @@ public static function getTestInfo($classname, $doc_comment = NULL) {
       throw new MissingGroupException(sprintf('Missing @group annotation in %s', $classname));
     }
     // Force all PHPUnit tests into the same group.
-    if (strpos($classname, 'Drupal\\Tests\\') === 0) {
+    if (static::isUnitTest($classname)) {
       $info['group'] = 'PHPUnit';
     }
     else {
@@ -408,6 +410,31 @@ public static function parseTestClassAnnotations(\ReflectionClass $class) {
   }
 
   /**
+   * Determines if the provided classname is a unit test.
+   *
+   * @param $classname
+   *   The test classname.
+   *
+   * @return bool
+   *   TRUE if the class is a unit test. FALSE if not.
+   */
+  public static function isUnitTest($classname) {
+    if (strpos($classname, 'Drupal\\Tests\\') === 0) {
+      $namespace = explode('\\', $classname);
+      $first_letter = Unicode::substr($namespace[2], 0, 1);
+      if (Unicode::strtoupper($first_letter) === $first_letter) {
+        // A core unit test.
+        return TRUE;
+      }
+      else if ($namespace[3] == 'Unit') {
+        // A module unit test
+        return TRUE;
+      }
+    }
+    return FALSE;
+  }
+
+  /**
    * Returns all available extensions.
    *
    * @return \Drupal\Core\Extension\Extension[]
diff --git a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
index e384a3c..c86933d 100644
--- a/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
+++ b/core/modules/simpletest/src/Tests/SimpleTestBrowserTest.php
@@ -138,11 +138,19 @@ public function testTestingThroughUI() {
 
     $this->drupalGet('admin/config/development/testing');
     $edit = array(
-      // A PHPUnit test.
+      // A PHPUnit unit test.
       'tests[Drupal\Tests\action\Unit\Menu\ActionLocalTasksTest]' => TRUE,
     );
     $this->drupalPostForm(NULL, $edit, t('Run tests'));
     $this->assertText('0 fails, 0 exceptions');
+
+    $this->drupalGet('admin/config/development/testing');
+    $edit = array(
+      // A PHPUnit functional test.
+      'tests[Drupal\Tests\simpletest\Functional\BrowserTestBaseTest]' => TRUE,
+    );
+    $this->drupalPostForm(NULL, $edit, t('Run tests'));
+    $this->assertText('0 fails, 0 exceptions');
   }
 
 }
diff --git a/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php b/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
index 03a87b7..4df976f 100644
--- a/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
+++ b/core/modules/simpletest/tests/src/Unit/TestInfoParsingTest.php
@@ -20,6 +20,7 @@ public function testTestInfoParser($expected, $classname, $doc_comment = NULL) {
   }
 
   public function infoParserProvider() {
+    // A module provided unit test.
     $tests[] = [
       // Expected result.
       [
@@ -31,6 +32,32 @@ public function infoParserProvider() {
       'Drupal\Tests\simpletest\Unit\TestInfoParsingTest',
     ];
 
+    // A core unit test.
+    $tests[] = [
+      // Expected result.
+      [
+        'name' => 'Drupal\Tests\Core\DrupalTest',
+        'group' => 'PHPUnit',
+        'description' => 'Tests \Drupal.',
+      ],
+      // Classname.
+      'Drupal\Tests\Core\DrupalTest',
+    ];
+
+    // Functional PHPUnit test.
+    $tests[] = [
+      // Expected result.
+      [
+        'name' => 'Drupal\Tests\simpletest\Functional\BrowserTestBaseTest',
+        'group' => 'simpletest',
+        'description' => 'Tests BrowserTestBase functionality.',
+      ],
+      // Classname.
+      'Drupal\Tests\simpletest\Functional\BrowserTestBaseTest',
+    ];
+
+    // Simpletest classes can not be autoloaded in a PHPUnit test, therefore
+    // provide a docblock.
     $tests[] = [
       // Expected result.
       [
diff --git a/core/phpunit.xml.dist b/core/phpunit.xml.dist
index 78f2f0e..2143771 100644
--- a/core/phpunit.xml.dist
+++ b/core/phpunit.xml.dist
@@ -10,10 +10,10 @@
   </php>
   <testsuites>
     <testsuite name="unit">
-      <directory>./tests</directory>
-      <directory>./modules/*/tests</directory>
-      <directory>../modules</directory>
-      <directory>../sites/*/modules</directory>
+      <directory>./tests/Drupal/Tests</directory>
+      <directory>./modules/*/tests/src/Unit</directory>
+      <directory>../modules/*/tests/src/Unit</directory>
+      <directory>../sites/*/modules/*/tests/src/Unit</directory>
       <!-- Exclude Composer's vendor directory so we don't run tests there. -->
       <exclude>./vendor</exclude>
       <!-- Exclude Drush tests. -->
@@ -23,6 +23,7 @@
     </testsuite>
     <testsuite name="functional">
       <directory>./modules/*/tests/src/Functional</directory>
+      <directory>./tests/Drupal/FunctionalTests</directory>
       <!-- Exclude Composer's vendor directory so we don't run tests there. -->
       <exclude>./vendor</exclude>
       <!-- Exclude Drush tests. -->