Add a method by which testcases can load necessary files via include_once.

There are a number of files that are only loaded when another function is called (for example, load a reporting class when displaying a widget). An autoloader would be the ideal way to handle this (both in production and for tests), but until PHP compatibility is sorted out this commit adds an easy fix:

Testcases can now populate the protected, static $includes property with filepaths relative to the project root; when the testcase boots up, these files will automatically be included.

tests/framework/class-wc-unit-test-case.php

@@ -12,6 +12,28 @@ class WC_Unit_Test_Case extends WP_UnitTestCase {
 	/** @var WC_Unit_Test_Factory instance */
 	protected $factory;
 
+	/**
+	 * Additional files, relative to the plugin's root directory, that should be explicitly included.
+	 *
+	 * @var array
+	 */
+	protected static $includes;
+
+	/**
+	 * If a test has declared include files, load them before running the tests in the class.
+	 *
+	 * @beforeClass
+	 */
+	public static function include_dependencies() {
+		$base_dir = trailingslashit( dirname( dirname( __DIR__ ) ) );
+
+		if ( ! empty( static::$includes ) ) {
+			foreach ( (array) static::$includes as $include ) {
+				include_once $base_dir . $include;
+			}
+		}
+	}
+
 	/**
 	 * Setup test case.
 	 *

tests/unit-tests/admin/reports/class-wc-tests-admin-report.php

@@ -11,13 +11,13 @@
 class WC_Tests_Admin_Report extends WC_Unit_Test_Case {
 
 	/**
-	 * Load the necessary files, as they're not automatically loaded by WooCommerce.
+	 * Additional files, relative to the plugin's root directory, that should be explicitly included.
 	 *
-	 * @beforeClass
+	 * @var array
 	 */
-	public static function includes() {
-		include_once WC_Unit_Tests_Bootstrap::instance()->plugin_dir . '/includes/admin/reports/class-wc-admin-report.php';
-	}
+	public static $includes = array(
+		'includes/admin/reports/class-wc-admin-report.php',
+	);
 
 	/**
 	 * Clear cached report data.