Add page test

This test will fail and return a 404 error code rather than
a 200 code as the page hasn't been built yet.

tests/src/Functional/PageListTest.php

@@ -11,4 +11,14 @@ class PageListTest extends BrowserTestBase {
    */
   protected static $modules = ['tdd_dublin'];
 
+  /**
+   * Test that the pages listing page exists and is accessible.
+   */
+  public function testListingPageExists() {
+    // Go to /pages and check that it is accessible by checking the status
+    // code.
+    $this->drupalGet('pages');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
 }