diff --git a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
index 75d68c2343..8f3f60a843 100644
--- a/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
+++ b/core/tests/Drupal/BuildTests/Framework/BuildTestBase.php
@@ -129,6 +129,15 @@ abstract class BuildTestBase extends TestCase {
    */
   private $locks;
 
+  /**
+   * The most recent command process.
+   *
+   * @var \Symfony\Component\Process\Process
+   *
+   * @see ::executeCommand()
+   */
+  private $commandProcess;
+
   /**
    * {@inheritdoc}
    */
@@ -182,7 +191,7 @@ protected function tearDown() {
    */
   protected function initMink() {
     // If the Symfony BrowserKit client can followMetaRefresh(), we should use
-    // its Goutte descendent instead of ours.
+    // the Goutte descendent instead of ours.
     if(method_exists(SymfonyClient::class, 'followMetaRefresh')) {
       $client = new Client;
     }
@@ -206,7 +215,7 @@ protected function initMink() {
    * request.
    *
    * @return \Behat\Mink\Mink
-   *   The Mink object for the last request.
+   *   The Mink object.
    */
   public function getMink() {
     return $this->mink;
@@ -225,78 +234,52 @@ public function getWorkspaceDirectory() {
   }
 
   /**
-   * Assert that text is present in the error output of a command.
+   * Assert that text is present in the error output of the most recent command.
    *
    * @param string $expected
    *   Text we expect to find in the error output of the command.
-   * @param string $command_line
-   *   Command line to execute.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
    */
-  public function assertCommandErrorOutputContains($expected, $command_line, $working_dir = NULL) {
-    $process = $this->assertCommand($command_line, $working_dir);
-    $this->assertContains($expected, $process->getErrorOutput());
-    return $process;
+  public function assertErrorOutputContains($expected) {
+    $this->assertContains($expected, $this->commandProcess->getErrorOutput());
   }
 
   /**
-   * Assert that text is present in the output of a command.
+   * Assert that text is present in the output of the most recent command.
    *
    * @param string $expected
    *   Text we expect to find in the output of the command.
-   * @param string $command_line
-   *   Command line to execute.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
    */
-  public function assertCommandOutputContains($expected, $command_line, $working_dir = NULL) {
-    $process = $this->assertCommand($command_line, $working_dir);
-    $this->assertContains($expected, $process->getOutput());
-    return $process;
+  public function assertCommandOutputContains($expected) {
+    $this->assertContains($expected, $this->commandProcess->getOutput());
   }
 
   /**
-   * Asserts that a command runs without error.
+   * Asserts that the last command ran without error.
    *
-   * This method runs the command and then asserts that the process exit code is
-   * 0.
+   * This assertion checks whether the last command returned an exit code of 0.
    *
    * If you need to assert a different exit code, then you can use
-   * executeCommand() and perform a different assertion.
+   * executeCommand() and perform a different assertion on the process object.
    *
    * @param string $command_line
    *   A command line to run in an isolated process.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
+   */
+  public function assertCommandSuccessful() {
+    return $this->assertCommandExitCode(0);
+  }
+
+  /**
+   * Asserts that the last command returned the specified exit code.
    *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
+   * @param int $expected_code
+   *   The expected process exit code.
    */
-  public function assertCommand($command_line, $working_dir = NULL) {
-    $this->assertNotEmpty($command_line);
-    $process = NULL;
-    try {
-      $process = $this->executeCommand($command_line, $working_dir);
-    }
-    catch (\Exception $ex) {
-      $this->fail('Process failed with message: ' . $ex->getMessage());
-    }
-    $this->assertEquals(0, $process->getExitCode(),
-      'COMMAND: ' . $command_line . "\n" .
-      'OUTPUT: ' . $process->getOutput() . "\n" .
-      'ERROR: ' . $process->getErrorOutput() . "\n"
+  public function assertCommandExitCode($expected_code) {
+    $this->assertEquals($expected_code, $this->commandProcess->getExitCode(),
+      'COMMAND: ' . $this->commandProcess->getCommandLine() . "\n" .
+      'OUTPUT: ' . $this->commandProcess->getOutput() . "\n" .
+      'ERROR: ' . $this->commandProcess->getErrorOutput() . "\n"
     );
-    return $process;
   }
 
   /**
@@ -315,34 +298,22 @@ public function executeCommand($command_line, $working_dir = NULL) {
     if ($working_dir) {
       $working_path .= '/' . $working_dir;
     }
-    $process = new Process($command_line);
-    $process->setWorkingDirectory($working_path)
+    $this->commandProcess = new Process($command_line);
+    $this->commandProcess->setWorkingDirectory($working_path)
       ->setTimeout(300)
       ->setIdleTimeout(300);
-    $process->run();
-    return $process;
+    $this->commandProcess->run();
+    return $this->commandProcess;
   }
 
   /**
-   * Assert a visit against an HTTP server using the given docroot.
-   *
-   * Use $this->getMink() to get session and assertion objects to test the
-   * result of this method.
+   * Helper function to assert that the last visit was a Drupal site.
    *
-   * @param string $request_uri
-   *   (optional) The non-host part of the URL. Example: some/path?foo=bar.
-   *   Defaults to visiting the homepage.
-   * @param int $expected_status_code
-   *   (optional) Expected HTTP status code for this request. Defaults to 200.
-   * @param string $docroot
-   *   (optional) Relative path within the test workspace file system that will
-   *   be the docroot for the request. Defaults to the workspace directory.
+   * This method asserts that the X-Generator header shows that the site is a
+   * Drupal site.
    */
-  public function assertVisit($request_uri = '/', $expected_status_code = 200, $docroot = NULL) {
-    $this->visit($request_uri, $docroot);
-    $actual_code = $this->mink->getSession()->getStatusCode();
-    $message = sprintf('Current response status code is %d, but %d expected for "%s".', $actual_code, $expected_status_code, $request_uri);
-    $this->assertEquals((int) $expected_status_code, $actual_code, $message);
+  public function assertDrupalVisit() {
+    $this->getMink()->assertSession()->responseHeaderMatches('X-Generator', '/Drupal \d+ \(https:\/\/www.drupal.org\)/');
   }
 
   /**
@@ -351,28 +322,29 @@ public function assertVisit($request_uri = '/', $expected_status_code = 200, $do
    * The concept here is that there could be multiple potential docroots in the
    * workspace, so you can use whichever ones you want.
    *
-   * Use $this->getMink() to get session and assertion objects to test the
-   * outcome of this method.
-   *
    * @param string $request_uri
    *   (optional) The non-host part of the URL. Example: /some/path?foo=bar.
    *   Defaults to visiting the homepage.
-   * @param string $docroot
+   * @param string $working_dir
    *   (optional) Relative path within the test workspace file system that will
    *   be the docroot for the request. Defaults to the workspace directory.
    *
+   * @return \Behat\Mink\Mink
+   *   The Mink object. Perform assertions against this.
+   *
    * @throws \InvalidArgumentException
    *   Thrown when $request_uri does not start with a slash.
    */
-  public function visit($request_uri = '/', $docroot = NULL) {
+  public function visit($request_uri = '/', $working_dir = NULL) {
     if ($request_uri[0] !== '/') {
-      throw new \InvalidArgumentException('URI: ' . $request_uri . ' should be relative. Example: /some/path?foo=bar');
+      throw new \InvalidArgumentException('URI: ' . $request_uri . ' must be relative. Example: /some/path?foo=bar');
     }
     // Try to make a server.
-    $this->standUpServer($docroot);
+    $this->standUpServer($working_dir);
 
     $request = 'http://localhost:' . $this->getPortNumber() . $request_uri;
     $this->mink->getSession()->visit($request);
+    return $this->mink;
   }
 
   /**
@@ -380,20 +352,20 @@ public function visit($request_uri = '/', $docroot = NULL) {
    *
    * Test authors should call visit() or assertVisit() instead.
    *
-   * @param string|null $docroot
+   * @param string|null $working_dir
    *   (optional) Server docroot relative to the workspace file system. Defaults
    *   to the workspace directory.
    */
-  protected function standUpServer($docroot = NULL) {
+  protected function standUpServer($working_dir = NULL) {
     // If the user wants to test a new docroot, we have to shut down the old
     // server process and generate a new port number.
-    if ($docroot !== $this->serverDocroot && !empty($this->serverProcess)) {
+    if ($working_dir !== $this->serverDocroot && !empty($this->serverProcess)) {
       $this->stopServer();
     }
     // If there's not a server at this point, make one.
-    $this->serverProcess = $this->instantiateServer($this->getPortNumber(), $docroot);
+    $this->serverProcess = $this->instantiateServer($this->getPortNumber(), $working_dir);
     if ($this->serverProcess) {
-      $this->serverDocroot = $docroot;
+      $this->serverDocroot = $working_dir;
     }
   }
 
@@ -406,7 +378,7 @@ protected function standUpServer($docroot = NULL) {
    *   The hostname for the server.
    * @param int $port
    *   The port number for the server.
-   * @param string|null $docroot
+   * @param string|null $working_dir
    *   (optional) Server docroot relative to the workspace filesystem. Defaults
    *   to the workspace directory.
    *
@@ -416,11 +388,11 @@ protected function standUpServer($docroot = NULL) {
    * @throws \RuntimeException
    *   Thrown if we were unable to start a web server.
    */
-  protected function instantiateServer($port, $docroot = NULL) {
+  protected function instantiateServer($port, $working_dir = NULL) {
     $finder = new PhpExecutableFinder();
     $full_docroot = $this->getWorkspaceDirectory();
-    if ($docroot) {
-      $full_docroot .= '/' . $docroot;
+    if ($working_dir) {
+      $full_docroot .= '/' . $working_dir;
     }
     $server = [
       $finder->find(),
diff --git a/core/tests/Drupal/BuildTests/Framework/BuildTestInterface.php b/core/tests/Drupal/BuildTests/Framework/BuildTestInterface.php
deleted file mode 100644
index 79e7b77ace..0000000000
--- a/core/tests/Drupal/BuildTests/Framework/BuildTestInterface.php
+++ /dev/null
@@ -1,180 +0,0 @@
-<?php
-
-namespace Drupal\BuildTests\Framework;
-
-/**
- * Provides a workspace to test build processes.
- *
- * If you need to build a file system and then run a command from the command
- * line then this is the test framework for you.
- *
- * Tests using this interface run in separate processes.
- *
- * Tests can perform HTTP requests against the assembled codebase.
- *
- * The results of these HTTP requests can be asserted using Mink.
- *
- * This framework does not use the same Mink extensions as BrowserTestBase.
- *
- * Features:
- * - Provide complete isolation between the test runner and the site under test.
- * - Provide a workspace where filesystem build processes can be performed.
- * - Allow for the use of PHP's build-in HTTP server to send requests to the
- *   site built using the filesystem.
- * - Allow for commands and HTTP requests to be made to different subdirectories
- *   of the workspace filesystem, to facilitate comparison between different
- *   build results, and to support Composer builds which have an alternate
- *   docroot.
- * - Provide as little framework as possible. Convenience methods should be
- *   built into the test, or abstract base classes.
- * - Allow parallel testing, using random/unique port numbers for different HTTP
- *   servers.
- *
- * @see \Drupal\BuildTests\Framework\BuildTestBase
- */
-interface BuildTestInterface {
-
-  /**
-   * Full path to the workspace where this test can build.
-   *
-   * This is often a directory within the system's temporary directory.
-   *
-   * @return string
-   *   Full path to the workspace where this test can build.
-   */
-  public function getWorkspaceDirectory();
-
-  /**
-   * Asserts that a command runs without error.
-   *
-   * This method runs the command and then asserts that the process exit code is
-   * 0.
-   *
-   * If you need to assert a different exit code, then you can use
-   * executeCommand() and perform a different assertion.
-   *
-   * @param string $command_line
-   *   A command line to run in an isolated process.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
-   */
-  public function assertCommand($command_line, $working_dir = NULL);
-
-  /**
-   * Assert that text is present in the error output of a command.
-   *
-   * @param string $expected
-   *   Text we expect to find in the error output of the command.
-   * @param string $command_line
-   *   Command line to execute.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
-   */
-  public function assertCommandErrorOutputContains($expected, $command_line, $working_dir = NULL);
-
-  /**
-   * Assert that text is present in the output of a command.
-   *
-   * @param string $expected
-   *   Text we expect to find in the output of the command.
-   * @param string $command_line
-   *   Command line to execute.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   *   The process that was used, for further assertion.
-   */
-  public function assertCommandOutputContains($expected, $command_line, $working_dir = NULL);
-
-  /**
-   * Run a command.
-   *
-   * @param string $command_line
-   *   A command line to run in an isolated process.
-   * @param string $working_dir
-   *   (optional) A working directory relative to the workspace, within which to
-   *   execute the command. Defaults to the workspace directory.
-   *
-   * @return \Symfony\Component\Process\Process
-   */
-  public function executeCommand($command_line, $working_dir = NULL);
-
-  /**
-   * Assert a visit against an HTTP server using the given docroot.
-   *
-   * Use $this->getMink() to get session and assertion objects to test the
-   * result of this method.
-   *
-   * @param string $request_uri
-   *   (optional) The non-host part of the URL. Example: some/path?foo=bar.
-   *   Defaults to visiting the homepage.
-   * @param int $expected_status_code
-   *   (optional) Expected HTTP status code for this request. Defaults to 200.
-   * @param string $docroot
-   *   (optional) Relative path within the test workspace file system that will
-   *   be the docroot for the request. Defaults to the workspace directory.
-   */
-  public function assertVisit($request_uri = '', $expected_status_code = 200, $docroot = NULL);
-
-  /**
-   * Get the Mink instance.
-   *
-   * Use the Mink object to perform assertions against the content returned by a
-   * request.
-   *
-   * @return \Behat\Mink\Mink
-   *   The Mink object for the last request.
-   */
-  public function getMink();
-
-  /**
-   * Visit a URI on the HTTP server.
-   *
-   * The concept here is that there could be multiple potential docroots in the
-   * workspace, so you can use whichever ones you want.
-   *
-   * Use $this->getMink() to get session and assertion objects to test the
-   * outcome of this method.
-   *
-   * @param string $request_uri
-   *   (optional) The non-host part of the URL. Example: /some/path?foo=bar.
-   *   Defaults to visiting the homepage.
-   * @param string $docroot
-   *   (optional) Relative path within the test workspace file system that will
-   *   be the docroot for the request. Defaults to the workspace directory.
-   *
-   * @throws \InvalidArgumentException
-   *   Thrown when $request_uri does not start with a slash.
-   */
-  public function visit($request_uri = '', $docroot = NULL);
-
-  /**
-   * Copy the current working codebase into a workspace.
-   *
-   * Use this method to copy the current codebase, including any patched
-   * changes, into the workspace.
-   *
-   * By default, the copy will exclude sites/default/settings.php,
-   * sites/default/files, and vendor/. Use the $iterator parameter to override
-   * this behavior.
-   *
-   * @param \Iterator|null $iterator
-   *   (optional) An iterator of all the files to copy. Default behavior is to
-   *   exclude site-specific directories and files.
-   * @param string|null $working_dir
-   *   (optional) Relative path within the test workspace file system that will
-   *   contain the copy of the codebase. Defaults to the workspace directory.
-   */
-  public function copyCodebase(\Iterator $iterator = NULL, $working_dir = NULL);
-
-}
diff --git a/core/tests/Drupal/BuildTests/QuickStart/InstallTest.php b/core/tests/Drupal/BuildTests/QuickStart/InstallTest.php
new file mode 100644
index 0000000000..acd46cdfcd
--- /dev/null
+++ b/core/tests/Drupal/BuildTests/QuickStart/InstallTest.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\BuildTests\QuickStart;
+
+/**
+ * Test whether we can install a Drupal site using the quickstart CLI.
+ *
+ * @group Build
+ * @group Command
+ * @group QuickStart
+ */
+class InstallTest extends QuickStartTestBase {
+
+  public function providerProfile() {
+    return [
+      'standard' => ['standard'],
+      'minimal' => ['minimal'],
+      'demo_umami' => ['demo_umami'],
+    ];
+  }
+
+  /**
+   * @dataProvider providerProfile
+   * @requires externalCommand composer
+   */
+  public function testInstall($profile) {
+    // Get the codebase.
+    $this->copyCodebase();
+
+    $this->executeCommand('COMPOSER_DISCARD_CHANGES=true composer install --no-dev --no-interaction');
+    $this->assertCommandSuccessful();
+    // Composer tells you stuff in error output.
+    $this->assertErrorOutputContains('Generating autoload files');
+    $this->installQuickStart($profile);
+
+    // Is the front page generated by Drupal?
+    $assert = $this->visit()->assertSession();
+    $assert->elementExists('css', 'html');
+    $this->assertDrupalVisit();
+
+    // Do we get 404 for a path that does not exist?
+    $this->visit('/does-not-exist')->assertSession()->statusCodeEquals(404);
+
+    // Can we log in and be an administrator?
+    $this->visit('/admin');
+    $assert->statusCodeEquals(403);
+    $this->formLogin($this->adminUsername, $this->adminPassword);
+    $this->visit('/admin');
+    $assert->statusCodeEquals(200);
+
+    // Can we try to be an admin even though we logged out?
+    $this->visit('/user/logout')->assertSession()->statusCodeEquals(200);
+    $this->visit('/admin');
+    $assert->statusCodeEquals(403);
+  }
+
+}
diff --git a/core/tests/Drupal/BuildTests/QuickStart/QuickStartTestBase.php b/core/tests/Drupal/BuildTests/QuickStart/QuickStartTestBase.php
new file mode 100644
index 0000000000..8a65675285
--- /dev/null
+++ b/core/tests/Drupal/BuildTests/QuickStart/QuickStartTestBase.php
@@ -0,0 +1,66 @@
+<?php
+
+namespace Drupal\BuildTests\QuickStart;
+
+use Drupal\BuildTests\Framework\BuildTestBase;
+use Symfony\Component\Process\PhpExecutableFinder;
+
+/**
+ * Helper methods for using the quickstart feature of Drupal.
+ */
+class QuickStartTestBase extends BuildTestBase {
+
+  /**
+   * User name of the admin account generated during install.
+   *
+   * @var string
+   */
+  protected $adminUsername;
+
+  /**
+   * Password of the admin account generated during install.
+   *
+   * @var string
+   */
+  protected $adminPassword;
+
+  /**
+   * Install a Drupal site using the quick start feature.
+   *
+   * @param string $profile
+   *   Drupal profile to install.
+   * @param string $working_dir
+   *   (optional) A working directory relative to the workspace, within which to
+   *   execute the command. Defaults to the workspace directory.
+   */
+  public function installQuickStart($profile, $working_dir = NULL) {
+    $finder = new PhpExecutableFinder();
+    $process = $this->executeCommand($finder->find() . ' ./core/scripts/drupal install ' . $profile, $working_dir);
+    $this->assertCommandSuccessful();
+    $this->assertCommandOutputContains('Username:');
+    preg_match('/Username: (.+)\vPassword: (.+)/', $process->getOutput(), $matches);
+    $this->assertNotEmpty($this->adminUsername = $matches[1]);
+    $this->assertNotEmpty($this->adminPassword = $matches[2]);
+  }
+
+  /**
+   * Helper that uses Drupal's user/login form to log in.
+   *
+   * @param string $username
+   *   Username.
+   * @param string $password
+   *   Password.
+   * @param string $working_dir
+   *   (optional) A working directory within which to login. Defaults to the
+   *   workspace directory.
+   */
+  public function formLogin($username, $password, $working_dir = NULL) {
+    $mink = $this->visit('/user/login', $working_dir);
+    $this->assertEquals(200, $mink->getSession()->getStatusCode());
+    $assert = $mink->assertSession();
+    $assert->fieldExists('edit-name')->setValue($username);
+    $assert->fieldExists('edit-pass')->setValue($password);
+    $mink->getSession()->getPage()->findButton('Log in')->submit();
+  }
+
+}