.../rest/tests/src/Functional/ResourceTestBase.php |  2 +-
 core/tests/Drupal/Tests/BrowserTestBase.php        | 33 ++++++++-
 .../Drupal/Tests/Core/Test/BrowserTestBaseTest.php | 82 ++++++++++++++++++++++
 3 files changed, 114 insertions(+), 3 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/ResourceTestBase.php b/core/modules/rest/tests/src/Functional/ResourceTestBase.php
index 0a0e34c..db7f25b 100644
--- a/core/modules/rest/tests/src/Functional/ResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/ResourceTestBase.php
@@ -335,7 +335,7 @@ protected function request($method, Url $url, array $request_options) {
     $request_options[RequestOptions::HTTP_ERRORS] = FALSE;
     $request_options[RequestOptions::ALLOW_REDIRECTS] = FALSE;
     $request_options = $this->decorateWithXdebugCookie($request_options);
-    $client = $this->getSession()->getDriver()->getClient()->getClient();
+    $client = $this->getHttpClient();
     return $client->request($method, $url->setAbsolute(TRUE)->toString(), $request_options);
   }
 
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index abdedd9..2507560 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -548,6 +548,33 @@ public function getSession($name = NULL) {
   }
 
   /**
+   * Obtain the HTTP client for the system under test.
+   *
+   * Use this method for arbitrary HTTP requests to the site under test. For
+   * most tests, you should not get the HTTP client and instead use navigation
+   * methods such as drupalGet() and clickLink() in order to benefit from
+   * assertions.
+   *
+   * Subclasses which substitute a different Mink driver should override this
+   * method and provide a Guzzle client if the Mink driver provides one.
+   *
+   * @return \GuzzleHttp\ClientInterface
+   *   The client with BrowserTestBase configuration.
+   *
+   * @throws \RuntimeException
+   *   If the Mink driver does not support a Guzzle HTTP client, throw an
+   *   exception.
+   */
+  protected function getHttpClient() {
+    /* @var $mink_driver \Behat\Mink\Driver\DriverInterface */
+    $mink_driver = $this->getSession()->getDriver();
+    if ($mink_driver instanceof GoutteDriver) {
+      return $mink_driver->getClient()->getClient();
+    }
+    throw new \RuntimeException ('The Mink client type ' . get_class($mink_driver) . ' does not support getHttpClient().');
+  }
+
+  /**
    * Returns WebAssert object.
    *
    * @param string $name
@@ -626,11 +653,13 @@ protected function buildUrl($path, array $options = []) {
    *   to set for example the "Accept-Language" header for requesting the page
    *   in a different language. Note that not all headers are supported, for
    *   example the "Accept" header is always overridden by the browser. For
-   *   testing REST APIs it is recommended to directly use an HTTP client such
-   *   as Guzzle instead.
+   *   testing REST APIs it is recommended to obtain a separate HTTP client
+   *   using getHttpClient() and performing requests that way.
    *
    * @return string
    *   The retrieved HTML string, also available as $this->getRawContent()
+   *
+   * @see \Drupal\Tests\BrowserTestBase::getHttpClient()
    */
   protected function drupalGet($path, array $options = [], array $headers = []) {
     $options['absolute'] = TRUE;
diff --git a/core/tests/Drupal/Tests/Core/Test/BrowserTestBaseTest.php b/core/tests/Drupal/Tests/Core/Test/BrowserTestBaseTest.php
new file mode 100644
index 0000000..a8eb65f
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Test/BrowserTestBaseTest.php
@@ -0,0 +1,82 @@
+<?php
+
+namespace Drupal\Tests\Core\Test;
+
+use Drupal\Tests\UnitTestCase;
+use Drupal\Tests\BrowserTestBase;
+use Behat\Mink\Driver\GoutteDriver;
+use Behat\Mink\Session;
+use Goutte\Client;
+
+/**
+ * @coversDefaultClass \Drupal\Tests\BrowserTestBase
+ * @group Test
+ */
+class BrowserTestBaseTest extends UnitTestCase {
+
+  protected function mockBrowserTestBaseWithDriver($driver) {
+    $session = $this->getMockBuilder(Session::class)
+      ->disableOriginalConstructor()
+      ->setMethods(['getDriver'])
+      ->getMock();
+    $session->expects($this->once())
+      ->method('getDriver')
+      ->willReturn($driver);
+
+    $btb = $this->getMockBuilder(BrowserTestBase::class)
+      ->disableOriginalConstructor()
+      ->setMethods(['getSession'])
+      ->getMockForAbstractClass();
+    $btb->expects($this->once())
+      ->method('getSession')
+      ->willReturn($session);
+
+    return $btb;
+  }
+
+  /**
+   * @covers ::getHttpClient
+   */
+  public function testGetHttpClient() {
+    // Our stand-in for the Guzzle client object.
+    $expected = new \stdClass();
+
+    $browserkit_client = $this->getMockBuilder(Client::class)
+      ->setMethods(['getClient'])
+      ->getMockForAbstractClass();
+    $browserkit_client->expects($this->once())
+      ->method('getClient')
+      ->willReturn($expected);
+
+    // Because the driver is a GoutteDriver, we'll get back a client.
+    $driver = $this->getMockBuilder(GoutteDriver::class)
+      ->setMethods(['getClient'])
+      ->getMock();
+    $driver->expects($this->once())
+      ->method('getClient')
+      ->willReturn($browserkit_client);
+
+    $btb = $this->mockBrowserTestBaseWithDriver($driver);
+
+    $ref_gethttpclient = new \ReflectionMethod($btb, 'getHttpClient');
+    $ref_gethttpclient->setAccessible(TRUE);
+
+    $this->assertSame(get_class($expected), get_class($ref_gethttpclient->invoke($btb)));
+  }
+
+  /**
+   * @covers ::getHttpClient
+   */
+  public function testGetHttpClientException() {
+    // A driver type that isn't GoutteDriver. This should cause a
+    // RuntimeException.
+    $btb = $this->mockBrowserTestBaseWithDriver(new \stdClass());
+
+    $ref_gethttpclient = new \ReflectionMethod($btb, 'getHttpClient');
+    $ref_gethttpclient->setAccessible(TRUE);
+
+    $this->setExpectedException(\RuntimeException::class, 'The Mink client type stdClass does not support getHttpClient().');
+    $ref_gethttpclient->invoke($btb);
+  }
+
+}