chai正在测试不应抛出typeerror的未定义项[重复]

必须将函数传递给 expect . 这样地:

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.'));

你这样做,是为了 期待 这个 结果 召唤的 model.get('z') . 但要测试是否抛出了某些内容,必须将函数传递给 期待 哪一个 期待 会自称。这个 bind 上面使用的方法创建一个新函数,当调用该函数时将调用 model.get 具有 this 设置为的值 model 第一个参数设置为 'z' .

很好的解释 绑定 可以找到 here .

AS this answer says ,您也可以将代码包装在匿名函数中,如下所示:

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

如果您已经在使用ES6/ES2015,那么您还可以使用箭头函数。它基本上与使用普通匿名函数相同,但更短。

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

这个问题有很多重复的地方,包括没有提到chai断言库的问题。以下是收集到的基本信息:

断言必须调用函数,而不是立即求值。

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

您可以使用任何断言库检查特定错误:

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./);

您必须处理“转义”测试的异常

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

一开始这看起来很混乱。就像骑自行车一样,一旦它发出“咔嚓”声,它就会永远发出“咔嚓”声。

示例来自 doc …;)

因为你依赖 这 语境 :

• 当函数被 投掷
• 它不可能知道这是什么

必须使用以下选项之一:

• 包 另一个函数内部的方法或函数调用

• 绑定 语境

  // 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
  

另一个可能的实现,比.bind()解决方案更麻烦,但是一个有助于说明expect()的点的实现需要一个提供 this 在所覆盖函数的上下文中,可以使用 call() 例如,

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