Add trait for mocking admin and super admin user

tests/php/src/Helpers/MockAdminUser.php

@@ -0,0 +1,36 @@
+<?php
+/**
+ * Trait MockAdminUser.
+ *
+ * @package AmpProject\AmpWP
+ */
+
+namespace AmpProject\AmpWP\Tests\Helpers;
+
+/**
+ * Helper trait for mocking an user:
+ * - Admin user in single site.
+ * - Super admin user in multisite.
+ *
+ * @package AmpProject\AmpWP
+ */
+trait MockAdminUser {
+
+	/**
+	 * Mock an admin or super admin user.
+	 */
+	public function mock_admin_user() {
+		if ( is_multisite() ) {
+			$user_id = self::factory()->user->create(
+				[
+					'role' => 'administrator',
+				]
+			);
+
+			grant_super_admin( $user_id );
+			wp_set_current_user( $user_id );
+		} else {
+			wp_set_current_user( self::factory()->user->create( [ 'role' => 'administrator' ] ) );
+		}
+	}
+}