Add an example module

web/modules/example/example.info.yml

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+name: Example
+type: module
+core_version_requirement: ^11

web/modules/example/example.routing.yml

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+example.page:
+  path: /example
+  defaults:
+    _controller: Drupal\example\Controller\ExamplePageController
+  methods: [GET]
+  requirements:
+    _permission: access content

web/modules/example/src/Controller/ExamplePageController.php

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+<?php
+
+namespace Drupal\example\Controller;
+
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
+final class ExamplePageController {
+
+  use StringTranslationTrait;
+
+  public function __invoke(): array {
+    return [
+      '#markup' => $this->t('This page is powered by Drupal and Nix.'),
+    ];
+  }
+
+}

web/modules/example/tests/src/Functional/ExampleTest.php

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+<?php
+
+namespace Drupal\Tests\example\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+class ExampleTest extends BrowserTestBase {
+
+  public $defaultTheme = 'stark';
+
+  public static $modules = [
+    'example',
+    'node',
+  ];
+
+  public function test_it_loads_the_page(): void {
+    $this->drupalGet('/example');
+
+    $assert = $this->assertSession();
+
+    $assert->statusCodeEquals(200);
+    $assert->pageTextContains('This page is powered by Drupal and Nix.');
+  }
+}