code: function defineMatcher(name, fn) {
      Expectation.prototype[name] =
          function () {
              let expectation = this;
              expectation.specification.description.log_(name);
              return fn.apply(expectation, arguments);
          };
      fn.toString = function () {
          return name;
      };
  }
docs: Matchers FUTURE: should not be used after endHook()