function toBeUndefined() {
      return {
        compare: function (actual) {
          return {
            pass: void 0 === actual,
          };
        },
      };
    }
{@link expect} the actual value to be `undefined`.
@function
@name matchers#toBeUndefined
@since 1.3.0
@example
expect(result).toBeUndefined():