Unit Tests: Added assertIsWPError to WC unit test framework

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

@@ -71,6 +71,16 @@ class WC_Unit_Test_Case extends WP_UnitTestCase {
 		$this->assertNotInstanceOf( 'WP_Error', $actual, $message );
 	}
 
+	/**
+	 * Asserts thing is WP_Error
+	 *
+	 * @param $actual
+	 * @param string $message
+	 */
+	public function assertIsWPError( $actual, $message = '' ) {
+		$this->assertInstanceOf( 'WP_Error', $actual, $message );
+	}
+
 	/**
 	 * Backport assertNotFalse to PHPUnit 3.6.12 which only runs in PHP 5.2
 	 *