diff --git a/tests/src/Unit/Template/ComponentsInfoTest.php b/tests/src/Unit/Template/ComponentsInfoTest.php
new file mode 100644
index 0000000..4bd3014
--- /dev/null
+++ b/tests/src/Unit/Template/ComponentsInfoTest.php
@@ -0,0 +1,362 @@
+<?php
+
+namespace Drupal\Tests\components\Unit\Template;
+
+use Drupal\components\Template\ComponentsInfo;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\components\Template\ComponentsInfo
+ * @group components
+ */
+class ComponentsInfoTest extends UnitTestCase {
+
+  /**
+   * The module extension list.
+   *
+   * @var \Drupal\Core\Extension\ModuleExtensionList|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $moduleExtensionList;
+
+  /**
+   * The theme extension list.
+   *
+   * @var \Drupal\Core\Extension\ThemeExtensionList|\PHPUnit_Framework_MockObject_MockObject
+   */
+  protected $themeExtensionList;
+
+  /**
+   * The system under test.
+   *
+   * @var \Drupal\components\Template\ComponentsInfo
+   */
+  protected $systemUnderTest;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    if (!constant('DRUPAL_MINIMUM_PHP')) {
+      define('DRUPAL_MINIMUM_PHP', '7.0.8');
+    }
+
+    $this->moduleExtensionList = $this->createMock('\Drupal\Core\Extension\ModuleExtensionList');
+    $this->themeExtensionList = $this->createMock('\Drupal\Core\Extension\ThemeExtensionList');
+  }
+
+  /**
+   * Creates a ComponentsInfo service after the dependencies are set up.
+   */
+  public function newSystemUnderTest() {
+    $this->systemUnderTest = new ComponentsInfo($this->moduleExtensionList, $this->themeExtensionList);
+  }
+
+  /**
+   * Tests finding components info from extension .info.yml files.
+   *
+   * Since this is a protected method, we are testing it via the constructor,
+   * getAllModuleInfo, and getProtectedNamespaces.
+   *
+   * @covers ::findComponentsInfo
+   */
+  public function testFindComponentsInfo() {
+    $this->moduleExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        // Does not have a components entry.
+        'system' => [
+          'no-components' => 'system-value',
+        ],
+        // Look for namespaces using 1.x API (backwards compatibility).
+        'harriet_tubman' => [
+          'component-libraries' => [
+            'harriet_tubman' => [
+              'paths' => ['deprecated'],
+            ],
+          ],
+        ],
+        'phillis_wheatley' => [
+          'components' => [
+            'namespaces' => [
+              // Namespace path is a string.
+              'phillis_wheatley' => 'templates',
+              // Namespace path is an array.
+              'wheatley' => ['components'],
+            ],
+          ],
+          // If components.namespaces is set, ignore 1.x API.
+          'component-libraries' => [
+            'wheatley' => [
+              'paths' => ['deprecated'],
+            ],
+          ],
+        ],
+        // No default namespace defined.
+        'edna_lewis' => [
+          'unrelatedKey' => 'should be ignored',
+          'components' => [
+            'includedKey' => 'included',
+            'namespaces' => [
+              'lewis' => ['templates', 'components'],
+            ],
+          ],
+        ],
+        // Manual opt-in.
+        'components' => [
+          'components' => [
+            'allow_default_namespace_reuse' => TRUE,
+          ],
+        ],
+      ]);
+    $this->moduleExtensionList->expects($this->exactly(5))
+      ->method('getPath')
+      ->willReturn('/system', '/tubman', '/wheatley', '/lewis', '/components');
+
+    $this->themeExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->newSystemUnderTest();
+
+    $expected = [
+      'harriet_tubman' => [
+        'namespaces' => [
+          'harriet_tubman' => ['/tubman/deprecated'],
+        ],
+        'extensionPath' => '/tubman',
+      ],
+      'phillis_wheatley' => [
+        'namespaces' => [
+          'phillis_wheatley' => ['/wheatley/templates'],
+          'wheatley' => ['/wheatley/components'],
+        ],
+        'extensionPath' => '/wheatley',
+      ],
+      'edna_lewis' => [
+        'includedKey' => 'included',
+        'namespaces' => [
+          'lewis' => ['/lewis/templates', '/lewis/components'],
+        ],
+        'extensionPath' => '/lewis',
+      ],
+      'components' => [
+        'allow_default_namespace_reuse' => TRUE,
+        'extensionPath' => '/components',
+      ],
+    ];
+    $result = $this->systemUnderTest->getAllModuleInfo();
+    $this->assertEquals($expected, $result);
+
+    $expected = ['system', 'edna_lewis'];
+    $result = $this->systemUnderTest->getProtectedNamespaces();
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Tests retrieving components info from a module.
+   *
+   * @covers ::getModuleInfo
+   */
+  public function testGetModuleInfo() {
+    $this->moduleExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        'foo' => [
+          'components' => [
+            'included' => 'foo',
+          ],
+        ],
+        'bar' => [
+          'components' => [
+            'included' => 'bar',
+          ],
+        ],
+      ]);
+    $this->moduleExtensionList
+      ->expects($this->exactly(2))
+      ->method('getPath')
+      ->willReturn('/foo', '/bar');
+
+    $this->themeExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->newSystemUnderTest();
+
+    $expected = [
+      'included' => 'bar',
+      'extensionPath' => '/bar',
+    ];
+    $result = $this->systemUnderTest->getModuleInfo('bar');
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Tests retrieving all components info from modules.
+   *
+   * @covers ::getAllModuleInfo
+   */
+  public function testGetAllModuleInfo() {
+    $this->moduleExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        'foo' => [
+          'no-components' => 'ignored',
+        ],
+        'bar' => [
+          'components' => [
+            'included' => 'not-ignored',
+          ],
+        ],
+      ]);
+    $this->moduleExtensionList
+      ->expects($this->exactly(2))
+      ->method('getPath')
+      ->willReturn('/foo', '/bar');
+
+    $this->themeExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->newSystemUnderTest();
+
+    $expected = [
+      'bar' => [
+        'included' => 'not-ignored',
+        'extensionPath' => '/bar',
+      ],
+    ];
+    $result = $this->systemUnderTest->getAllModuleInfo();
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Tests retrieving components info from a theme.
+   *
+   * @covers ::getThemeInfo
+   */
+  public function testGetThemeInfo() {
+    $this->moduleExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->themeExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        'foo' => [
+          'components' => [
+            'included' => 'foo',
+          ],
+        ],
+        'bar' => [
+          'components' => [
+            'included' => 'bar',
+          ],
+        ],
+      ]);
+    $this->themeExtensionList
+      ->expects($this->exactly(2))
+      ->method('getPath')
+      ->willReturn('/foo', '/bar');
+
+    $this->newSystemUnderTest();
+
+    $expected = [
+      'included' => 'bar',
+      'extensionPath' => '/bar',
+    ];
+    $result = $this->systemUnderTest->getThemeInfo('bar');
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Tests retrieving all components info from themes.
+   *
+   * @covers ::getAllThemeInfo
+   */
+  public function testGetAllThemeInfo() {
+    $this->moduleExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->themeExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        'foo' => [
+          'no-components' => 'ignored',
+        ],
+        'bar' => [
+          'components' => [
+            'included' => 'not-ignored',
+          ],
+        ],
+      ]);
+    $this->themeExtensionList
+      ->expects($this->exactly(2))
+      ->method('getPath')
+      ->willReturn('/foo', '/bar');
+
+    $this->newSystemUnderTest();
+
+    $expected = [
+      'bar' => [
+        'included' => 'not-ignored',
+        'extensionPath' => '/bar',
+      ],
+    ];
+    $result = $this->systemUnderTest->getAllThemeInfo();
+    $this->assertEquals($expected, $result);
+  }
+
+  /**
+   * Tests retrieving protected namespaces.
+   *
+   * @covers ::getProtectedNamespaces
+   */
+  public function testGetProtectedNamespaces() {
+    $this->moduleExtensionList
+      ->expects($this->exactly(1))
+      ->method('getAllInstalledInfo')
+      ->willReturn([
+        'foo' => [
+          'no-components' => 'system-value',
+        ],
+        'bar' => [
+          'no-components' => 'system-value',
+        ],
+        'baz' => [
+          'no-components' => 'system-value',
+        ],
+        'bop' => [
+          'no-components' => 'system-value',
+        ],
+        // Manual opt-in.
+        'mmmbop' => [
+          'components' => [
+            'allow_default_namespace_reuse' => TRUE,
+          ],
+        ],
+      ]);
+    $this->moduleExtensionList->expects($this->exactly(5))
+      ->method('getPath')
+      ->willReturn('/some-path');
+
+    $this->themeExtensionList
+      ->method('getAllInstalledInfo')
+      ->willReturn([]);
+
+    $this->newSystemUnderTest();
+
+    $expected = ['foo', 'bar', 'baz', 'bop'];
+    $result = $this->systemUnderTest->getProtectedNamespaces();
+    $this->assertEquals($expected, $result);
+  }
+
+}