Add lesson 4

- Add initial `PostNodeRepository`
- Move logic to Repository
- Inject `EntityTypeManagerInterface`
- Add `PostNodeRepositoryTest`
- Add failing test method
- Failing test: non-existent service
- The "node" entity type does not exist.
- Create posts
- Add assertions based on the `created` date
- Sort nodes before returning them
- Return values to reset array keys

web/modules/custom/example/tests/src/Kernel/PostNodeRepositoryTest.php

@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\Tests\example\Kernel;
+
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\example\Repository\PostNodeRepository;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\node\NodeInterface;
+use Drupal\Tests\node\Traits\NodeCreationTrait;
+
+class PostNodeRepositoryTest extends EntityKernelTestBase {
+
+  use NodeCreationTrait;
+
+  protected static $modules = ['node', 'example'];
+
+  public function testPostsAreReturnedByCreatedDate(): void {
+    // Arrange.
+    $this->createNode([
+      'title' => 'Post one',
+      'created' => (new DrupalDateTime('-1 week'))->getTimestamp(),
+      'type' => 'post',
+    ]);
+
+    $this->createNode([
+      'title' => 'Post two',
+      'created' => (new DrupalDateTime('-8 days'))->getTimestamp(),
+      'type' => 'post',
+    ]);
+
+    $this->createNode([
+      'title' => 'Post three',
+      'created' => (new DrupalDateTime('yesterday'))->getTimestamp(),
+      'type' => 'post',
+    ]);
+
+    // Act.
+    $postRepository = $this->container->get(PostNodeRepository::class);
+    assert($postRepository instanceof PostNodeRepository);
+    $nodes = $postRepository->findAll();
+
+    // Assert.
+    self::assertCount(3, $nodes);
+
+    self::assertSame(
+      ['Post two', 'Post one', 'Post three'],
+      array_map(
+        fn (NodeInterface $node) => $node->label(),
+        $nodes
+      )
+    );
+  }
+
+}