[英]test for error thrown in node.js using mocha chai
I'm new to node.js, and I'm having problems setting up a simple unit test for a function I expect to throw an error.我是 node.js 的新手,我在为 function 设置简单的单元测试时遇到问题,我预计会引发错误。 My function is very simple:我的 function 很简单:
const which_min = function(array) {
var lowest = 0;
for (var i = 1; i < array.length; i++) {
if (array[i] < array[lowest]) lowest = i;
}
return lowest;
}
I want to test if my function tosses an error when no argument is passed to it.我想测试我的 function 在没有参数传递给它时是否抛出错误。 In my test folder I have a test file在我的测试文件夹中,我有一个测试文件
var assert = require('chai').assert;
var expect = require('chai').expect;
describe('#which_min()', function() {
context('with incorrect arguments', function() {
it('errorTest', function() {
expect(function(){utils.which_min();}).to.throw(new TypeError("Cannot read property 'length' of undefined"))
})
})
})
But I get what I find to be a quite peculiar error:但是我发现了一个非常特殊的错误:
AssertionError: expected [Function] to throw 'TypeError: Cannot read property \'length\' of undefined' but 'TypeError: Cannot read property \'length\' of undefined' was thrown
+ expected - actual
I really do not see the difference in what I expect and what I get - so why do I not pass the test here?我真的看不出我所期望的和我得到的有什么不同——那么为什么我在这里没有通过测试呢? I expect it to be something with quotation marks?我希望它是带引号的东西?
Thanks /Kira谢谢/基拉
You are passing a new instance of TypeError
to the expect()
function, which means it will expect your which_min()
function to throw that exact error instance (but it won't do that, it will throw another instance of the same error type with the same error message).您正在将TypeError
的新实例传递给expect()
function,这意味着它将期望您的which_min()
function 抛出该确切的错误实例(但它不会这样做,它会抛出相同错误类型的另一个实例具有相同的错误消息)。
Try just passing the error string instead, so:尝试只传递错误字符串,所以:
var assert = require('chai').assert;
var expect = require('chai').expect;
describe('#which_min()', function() {
context('with incorrect arguments', function() {
it('errorTest', function() {
expect(function(){utils.which_min();}).to.throw("Cannot read property 'length' of undefined")
})
})
})
In that case, Chai will expect any error type with the same error message to be thrown.在这种情况下,Chai 将期望抛出具有相同错误消息的任何错误类型。
You could also choose to assert that the error is a TypeError
like this:您还可以选择断言错误是TypeError
,如下所示:
var assert = require('chai').assert;
var expect = require('chai').expect;
describe('#which_min()', function() {
context('with incorrect arguments', function() {
it('errorTest', function() {
expect(function(){utils.which_min();}).to.throw(TypeError)
})
})
})
But then you aren't asserting that the error message is exactly what you expect.但是,您并没有断言错误消息正是您所期望的。
Refer to the official Chai documentation here for more info: https://www.chaijs.com/api/bdd/#method_throw有关更多信息,请参阅此处的官方 Chai 文档: https://www.chaijs.com/api/bdd/#method_throw
EDIT:编辑:
As @Sree.Bh mentions, you can also pass both the expected type of the error and the expected error message to the throw()
assertion, like so:正如@Sree.Bh 所提到的,您还可以将预期的错误类型和预期的错误消息传递给throw()
断言,如下所示:
var assert = require('chai').assert;
var expect = require('chai').expect;
describe('#which_min()', function() {
context('with incorrect arguments', function() {
it('errorTest', function() {
expect(function(){utils.which_min();}).to.throw(TypeError, "Cannot read property 'length' of undefined")
})
})
})
Agree to @krisloekkegaard explanation why expect(function(){utils.which_min();}).to.throw(new TypeError("Cannot read property 'length' of undefined"))
fails:同意@krisloekkegaard 解释为什么expect(function(){utils.which_min();}).to.throw(new TypeError("Cannot read property 'length' of undefined"))
失败:
To check the 'error type' and the 'message', use :要检查“错误类型”和“消息”,请使用:
expect(function () { utils.which_min(); })
.to.throw(TypeError, "Cannot read property 'length' of undefined");
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.