Mocha / Chai期待 . 没有 grab 抛出的错误

6 回答

• 147

  你必须将一个函数传递给 expect . 像这样：

  expect(model.get.bind(model, 'z')).to.throw('Property does not exist in model schema.');
  expect(model.get.bind(model, 'z')).to.throw(new Error('Property does not exist in model schema.'));
  

  你正在这样做，你传递给 expect 调用 model.get('z') 的结果 . 但是为了测试是否抛出某些东西，你必须将一个函数传递给 expect ， expect 将调用它自己 . 上面使用的 bind 方法创建一个新函数，调用时将调用 model.get ，其中 this 设置为 model ，第一个参数设置为 'z' .

  可以找到 bind 的一个很好的解释here .

  回复于 2024-04-27T13:47:22+08:00
• 59

  作为this answer says，您也可以将代码包装在这样的匿名函数中：

  expect(function(){
      model.get('z');
  }).to.throw('Property does not exist in model schema.');
  

  回复于 2024-04-27T13:47:22+08:00
• 3

  如果您已经在使用ES6 / ES2015，那么您也可以使用箭头功能 . 它与使用普通匿名函数基本相同，但更短 .

  expect(() => model.get('z')).to.throw('Property does not exist in model schema.');
  

  回复于 2024-04-27T13:47:22+08:00
• 281

  这个问题有许多重复，包括没有提到Chai断言库的问题 . 以下是收集在一起的基础知识：

  The assertion must call the function, instead of it evaluating immediately.

  assert.throws(x.y.z);      
     // FAIL.  x.y.z throws an exception, which immediately exits the
     // enclosing block, so assert.throw() not called.
  assert.throws(()=>x.y.z);  
     // assert.throw() is called with a function, which only throws
     // when assert.throw executes the function.
  assert.throws(function () { x.y.z });   
     // if you cannot use ES6 at work
  function badReference() { x.y.z }; assert.throws(badReference);  
     // for the verbose
  assert.throws(()=>model.get(z));  
     // the specific example given.
  homegrownAssertThrows(model.get, z);
     //  a style common in Python, but not in JavaScript
  

  You can check for specific errors using any assertion library:

  Node

  assert.throws(() => x.y.z);
    assert.throws(() => x.y.z, ReferenceError);
    assert.throws(() => x.y.z, ReferenceError, /is not defined/);
    assert.throws(() => x.y.z, /is not defined/);
    assert.doesNotThrow(() => 42);
    assert.throws(() => x.y.z, Error);
    assert.throws(() => model.get.z, /Property does not exist in model schema./)
  

  Should

  should.throws(() => x.y.z);
    should.throws(() => x.y.z, ReferenceError);
    should.throws(() => x.y.z, ReferenceError, /is not defined/);
    should.throws(() => x.y.z, /is not defined/);
    should.doesNotThrow(() => 42);
    should.throws(() => x.y.z, Error);
    should.throws(() => model.get.z, /Property does not exist in model schema./)
  

  Chai Expect

  expect(() => x.y.z).to.throw();
    expect(() => x.y.z).to.throw(ReferenceError);
    expect(() => x.y.z).to.throw(ReferenceError, /is not defined/);
    expect(() => x.y.z).to.throw(/is not defined/);
    expect(() => 42).not.to.throw();
    expect(() => x.y.z).to.throw(Error);
    expect(() => model.get.z).to.throw(/Property does not exist in model schema./);
  

  You must handle exceptions that 'escape' the test

  it('should handle escaped errors', function () {
    try {
      expect(() => x.y.z).not.to.throw(RangeError);
    } catch (err) {
      expect(err).to.be.a(ReferenceError);
    }
  });
  

  起初这看起来很混乱 . 就像骑自行车一样，只需点击一下就可以“点击” .

  回复于 2024-04-27T13:47:22+08:00
• 1

  来自doc ......;的例子

  因为你依赖 this context ：

  • 在 .throw 调用该函数时丢失

  • 没有办法知道它应该是什么

  你必须使用以下选项之一：

  • wrap 另一个函数内部的方法或函数调用

  • bind 上下文

  // wrap the method or function call inside of another function
  expect(function () { cat.meow(); }).to.throw();  // Function expression
  expect(() => cat.meow()).to.throw();             // ES6 arrow function
  
  // bind the context
  expect(cat.meow.bind(cat)).to.throw();           // Bind
  

  回复于 2024-04-27T13:47:22+08:00
• 73

  另一个可能的实现，比.bind（）解决方案更麻烦，但有一个有助于使expect（）需要一个为覆盖函数提供 this 上下文的函数，你可以使用 call() ，例如，

  expect(function() {model.get.call(model, 'z');}).to.throw('...');

  回复于 2024-04-27T13:47:22+08:00