如何在mocha的mocha.opts文件中添加chaijs的断言？

Question

I don't know if this is even possible. I know if we just use should.js library we can do the following in mocha.opts file

--require should

But since chai is a parent module and assert is sub-module of chai , how do I require it in mocha.opts file?

Or am I missing something really basic?

Answer 1

AFAIK chai and mocha are not compatible in this way. It only works with should because should modifies the prototypes of the built-in objects, which some folks find acceptable for this particular use case but in general it is regarded as a bad practice to be avoided.

What you can do instead is write your own little wrapper module that does this:

global.assert = require('chai').assert;

And then in your mocha.opts you can do --require global-chai-assert and your tests will have access to chai's assert function as a global. I personally think this is an antipattern, but if you like it, that's how I'd do it.

Answer 2

Since chai v4.0.0 you can register assert/expect/should globals like this:

require('chai/register-assert');  // Using Assert style
require('chai/register-expect');  // Using Expect style
require('chai/register-should');  // Using Should style

So you can add it to your mocha.opts:

--require chai/register-should

There are some usage examples on the chai's repo README .