diff --git a/core/modules/user/src/Tests/UserDataTest.php b/core/modules/user/src/Tests/UserDataTest.php
new file mode 100644
index 0000000000..34b4ed2935
--- /dev/null
+++ b/core/modules/user/src/Tests/UserDataTest.php
@@ -0,0 +1,98 @@
+<?php
+
+namespace Drupal\user\Tests;
+
+use Drupal\Core\Database\Driver\fake\FakeConnection;
+use Drupal\Tests\UnitTestCase;
+use Drupal\user\UserData;
+
+/**
+ * Tests the user.data service.
+ *
+ * @group user
+ * @see \Drupal\user\UserData
+ */
+class UserDataTest extends UnitTestCase {
+
+  /**
+   * Tests get method.
+   *
+   * @see \Drupal\user\UserData::get()
+   */
+  public function testGetMethod() {
+    $database_contents = array('users_data' => $this->getDummyUserData());
+    $connection = $this->getDatabase($database_contents);
+    $user_data = new UserData($connection);
+
+    // 1. Get all data of given module.
+    $expected = array();
+    $actual = $user_data->get('foo_module');
+    $this->assertSame($expected, $actual);
+
+    // 2. set just uid.
+    $user_data->get('foo_module', 1);
+
+    // 3. set just name.
+    $user_data->get('foo_module', NULL, 'key1');
+
+    // 4. set both uid and name.
+    $user_data->get('foo_module', 2, 'key2');
+  }
+
+  /**
+   * Get a fake database connection object for use in tests.
+   *
+   * @param array $database_contents
+   *   The database contents faked as an array. Each key is a table name, each
+   *   value is a list of table rows, an associative array of field => value.
+   * @param array $connection_options
+   *   (optional) The array of connection options for the database.
+   * @param string $prefix
+   *   (optional) The table prefix on the database.
+   *
+   * @return \Drupal\Core\Database\Driver\fake\FakeConnection
+   *   The database connection.
+   */
+  protected function getDatabase(array $database_contents, $connection_options = array(), $prefix = '') {
+    return new FakeConnection($database_contents, $connection_options, $prefix);
+  }
+
+  /**
+   * Dummy data.
+   *
+   * @return array
+   */
+  protected function getDummyUserData() {
+    return array(
+      array(
+        'module' => 'foo_module',
+        'uid' => 1,
+        'name' => 'key1',
+        'value' => 'value1',
+        'serialized' => FALSE
+      ),
+      array(
+        'module' => 'foo_module',
+        'uid' => 2,
+        'name' => 'key2',
+        'value' => 'value2',
+        'serialized' => FALSE
+      ),
+      array(
+        'module' => 'foo_module',
+        'uid' => 3,
+        'name' => 'key3',
+        'value' => 'value3',
+        'serialized' => FALSE
+      ),
+      array(
+        'module' => 'bar_module',
+        'uid' => 1,
+        'name' => 'key1',
+        'value' => 'value1',
+        'serialized' => FALSE
+      ),
+    );
+  }
+
+}