text: function shouldThrow(func, errorMessage) {
      var errorThrown = false;
      var error = null;
      try {
          func();
      } catch (e) {
          errorThrown = true;
          error = e;
      }
      if (!errorThrown)
          throw new Error('not thrown');
      if (String(error) !== errorMessage)
          throw new Error(`bad error: ${String(error)}`);
  }
  
  
  shouldThrow(function () {
      class A extends A {
      }
  }, `ReferenceError: Cannot access uninitialized variable.`);
  