feat: add an example module with custom tests

Add a custom module based on my Drupal module template:

https://github.com/opdavies/drupal-module-template

web/modules/custom/example/tests/src/Functional/ExamplePageTest.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\Tests\example\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Symfony\Component\HttpFoundation\Response;
+
+final class ExamplePageTest extends BrowserTestBase {
+
+  public $defaultTheme = 'stark';
+
+  protected static $modules = [
+    // Core.
+    'node',
+
+    // Custom.
+    "example"
+  ];
+
+  /** @test */
+  public function should_load_the_example_page_for_anonymous_users(): void {
+    // Arrange.
+
+    // Act.
+    $this->drupalGet('/@opdavies/drupal-module-template');
+
+    // Assert.
+    $this->assertSession()->statusCodeEquals(Response::HTTP_OK);
+  }
+
+}