_match = function (cssCode, tagInfo, mode) {
            lastCssCode = cssCode;
            try {
                return _findMatchingRules(cssCode, tagInfo, mode);
            } catch (e) {
                this.fail(e.message + ": " + cssCode);
                return [];
            }
        }
Test helper function; tagInfo object contains one of: tag, id, clazz. Tests against only
the given cssCode string in isolation (no CSS files are loaded). If tagInfo not specified,
returns no results; only tests that parsing plus a simple search won't crash.