diff --git a/core/tests/Drupal/KernelTests/Core/Block/BlockManagerTest.php b/core/tests/Drupal/KernelTests/Core/Block/BlockManagerTest.php
deleted file mode 100644
index ff8cfb1..0000000
--- a/core/tests/Drupal/KernelTests/Core/Block/BlockManagerTest.php
+++ /dev/null
@@ -1,91 +0,0 @@
-<?php
-
-namespace Drupal\KernelTests\Core\Block;
-
-use Drupal\Core\Block\Plugin\Block\Broken;
-use Drupal\Core\Block\Plugin\Block\PageTitleBlock;
-use Drupal\Core\Menu\Plugin\Block\LocalActionsBlock;
-use Drupal\Core\Menu\Plugin\Block\LocalTasksBlock;
-use Drupal\KernelTests\KernelTestBase;
-
-/**
- * @coversDefaultClass \Drupal\Core\Block\BlockManager
- *
- * @group block
- */
-class BlockManagerTest extends KernelTestBase {
-
-  /**
-   * The available block definitions.
-   *
-   * @var array
-   */
-  protected $blockDefinitions = [
-    'broken' => [
-      'admin_label' => 'Broken/Missing',
-      'category' => 'Block',
-      'id' => 'broken',
-      'class' => Broken::class,
-      'provider' => 'core',
-    ],
-    'page_title_block' => [
-      'admin_label' => 'Page title',
-      'category' => 'core',
-      'id' => 'page_title_block',
-      'class' => PageTitleBlock::class,
-      'provider' => 'core',
-    ],
-    'local_actions_block' => [
-      'admin_label' => 'Primary admin actions',
-      'category' => 'core',
-      'id' => 'local_actions_block',
-      'class' => LocalActionsBlock::class,
-      'provider' => 'core',
-    ],
-    'local_tasks_block' => [
-      'admin_label' => 'Tabs',
-      'category' => 'core',
-      'id' => 'local_tasks_block',
-      'class' => LocalTasksBlock::class,
-      'provider' => 'core',
-    ],
-  ];
-
-  /**
-   * @covers ::getDefinitions
-   */
-  public function testDefinitions() {
-    $expected = $this->blockDefinitions;
-    $definitions = \Drupal::service('plugin.manager.block')->getDefinitions();
-    $this->assertEquals($expected, $definitions);
-  }
-
-  /**
-   * @covers ::getSortedDefinitions
-   */
-  public function testSortedDefinitions() {
-    $expected = $this->blockDefinitions;
-    // Do not include the 'broken' plugin.
-    unset($expected['broken']);
-
-    $definitions = \Drupal::service('plugin.manager.block')->getSortedDefinitions();
-    $this->assertEquals($expected, $definitions);
-    // Ensure the order is as expected.
-    $this->assertSame(array_keys($expected), array_keys($definitions));
-  }
-
-  /**
-   * @covers ::getGroupedDefinitions
-   */
-  public function testGroupedDefinitions() {
-    $expected = $this->blockDefinitions;
-    // Do not include the 'broken' plugin.
-    unset($expected['broken']);
-    // Group the plugins by their category.
-    $expected = ['core' => $expected];
-
-    $definitions = \Drupal::service('plugin.manager.block')->getGroupedDefinitions();
-    $this->assertEquals($expected, $definitions);
-  }
-
-}
diff --git a/core/tests/Drupal/Tests/Core/Block/BlockManagerTest.php b/core/tests/Drupal/Tests/Core/Block/BlockManagerTest.php
new file mode 100644
index 0000000..796146d
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Block/BlockManagerTest.php
@@ -0,0 +1,87 @@
+<?php
+
+namespace Drupal\Tests\Core\Block;
+
+use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
+use Drupal\Core\Block\BlockManager;
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\Block\BlockManager
+ *
+ * @group block
+ */
+class BlockManagerTest extends UnitTestCase {
+
+  /**
+   * The block manager under test.
+   *
+   * @var \Drupal\Core\Block\BlockManager
+   */
+  protected $blockManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $cache_backend = $this->prophesize(CacheBackendInterface::class);
+    $module_handler = $this->prophesize(ModuleHandlerInterface::class);
+    $this->blockManager = new BlockManager(new \ArrayObject(), $cache_backend->reveal(), $module_handler->reveal());
+
+    $discovery = $this->prophesize(DiscoveryInterface::class);
+    // Specify the 'broken' block, as well as 3 other blocks with admin labels
+    // that are purposefully not in alphabetical order.
+    $discovery->getDefinitions()->willReturn([
+      'broken' => [
+        'admin_label' => 'Broken/Missing',
+        'category' => 'Block',
+      ],
+      'block1' => [
+        'admin_label' => 'Coconut',
+        'category' => 'expected_category',
+      ],
+      'block2' => [
+        'admin_label' => 'Apple',
+        'category' => 'expected_category',
+      ],
+      'block3' => [
+        'admin_label' => 'Banana',
+        'category' => 'expected_category',
+      ],
+    ]);
+    // Force the discovery object onto the block manager.
+    $property = new \ReflectionProperty(BlockManager::class, 'discovery');
+    $property->setAccessible(TRUE);
+    $property->setValue($this->blockManager, $discovery->reveal());
+  }
+
+  /**
+   * @covers ::getDefinitions
+   */
+  public function testDefinitions() {
+    $definitions = $this->blockManager->getDefinitions();
+    $this->assertSame(['broken', 'block1', 'block2', 'block3'], array_keys($definitions));
+  }
+
+  /**
+   * @covers ::getSortedDefinitions
+   */
+  public function testSortedDefinitions() {
+    $definitions = $this->blockManager->getSortedDefinitions();
+    $this->assertSame(['block2', 'block3', 'block1'], array_keys($definitions));
+  }
+
+  /**
+   * @covers ::getGroupedDefinitions
+   */
+  public function testGroupedDefinitions() {
+    $definitions = $this->blockManager->getGroupedDefinitions();
+    $this->assertArrayHasKey('expected_category', $definitions);
+    $this->assertSame(['block2', 'block3', 'block1'], array_keys($definitions['expected_category']));
+  }
+
+}