Add tests for domain argument

See #7.

features/makepot-plugin.feature

@@ -74,3 +74,42 @@ Feature: Generate a POT file of a WordPress plugin
       "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
       "Language-Team: LANGUAGE <LL@li.org>\n"
       """
+
+  Scenario: Ignores any other text domain
+    Given an empty foo-plugin directory
+    And a foo-plugin/foo-plugin.php file:
+      """
+      <?php
+      /**
+       * Plugin Name: Foo Plugin
+       * Plugin URI:  https://example.com
+       * Description:
+       * Version:     0.1.0
+       * Author:
+       * Author URI:
+       * License:     GPL-2.0+
+       * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
+       * Text Domain: foo-plugin
+       * Domain Path: /languages
+       */
+
+       __( 'Hello World', 'foo-plugin' );
+
+       __( 'Foo', 'bar' );
+
+       __( 'bar' );
+      """
+
+    When I run `wp makepot plugin foo-plugin foo-plugin.pot`
+    And the foo-plugin.pot file should contain:
+      """
+      msgid "Hello World"
+      """
+    And the foo-plugin.pot file should not contain:
+      """
+      msgid "Foo"
+      """
+    And the foo-plugin.pot file should not contain:
+      """
+      msgid "bar"
+      """