Add initial test file for WC_Register_Legacy_Settings, with test for constructor.

tests/unit-tests/settings/register-legacy-settings.php

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * Settings API Tests
+ * @package WooCommerce\Tests\Settings
+ * @since 2.7.0
+ */
+class WC_Tests_Register_Legacy_Settings extends WC_Unit_Test_Case {
+
+	/**
+	 * @var WC_Settings_Page $page
+	 */
+	protected $page;
+
+	/**
+	 * Initialize a WC_Settings_Page for testing
+	 */
+	public function setUp() {
+		parent::setUp();
+
+		$this->page = new WC_Settings_General(); 
+	}
+
+	public function test_constructor() {
+		
+		$legacy_settings = new WC_Register_Legacy_Settings( $this->page );
+		
+		$this->assertEquals( has_filter( 'woocommerce_settings_groups', array( $legacy_settings, 'register_legacy_group' ) ), 10 );
+		$this->assertEquals( has_filter( 'woocommerce_settings-' . $this->page->get_id(), array( $legacy_settings, 'register_legacy_settings' ) ), 10 );
+	}
+
+}