Prevent tests from polluting required modules when running Mocha for multiple test files

Question

I have a lib.js that I will require and test in 2 tests, test1.js and test2.js (using mocha and should.js):

lib.js simply exports a data object:

module.exports.data = {};

test1.js looks like this:

var data = require('./lib.js').data;                                                    

describe('.data', function() {                                                          
  it('should be able to add data', function() {                                         
    data.entry = 'random data';                                                         
    console.log(data);  // expecting to get `{ entry: 'random data' }`                                                                  
  })                                                                                    
})

And test2.js looks like this:

var data = require('./lib.js').data;

describe('.data', function() {
  it('should have empty data', function() {
    console.log(data);  // expecting to get `{}`
  })
})

If I run mocha with multiple files, like mocha test1.js test2.js, both would print { entry: 'random data' }, and it would be undesired that running tests together gets different results from running them separately.

I believe this is because of node caching the modules, and I could restore the module before leaving the test. However, since this behavior might happen easily when writing tests, I wonder what the correct strategy is. Maybe there is something I can do on the Mocha level? Thanks a lot!

possible duplicate of [How to require same file in Mocha test](http://stackoverflow.com/questions/22975864/how-to-require-same-file-in-mocha-test) — Louis, Aug 25 '14 at 23:11
Thanks, @Louis. That is helpful. I guess my question would be multiple test files. Ideally, I should be able to work on my own tests without worrying about others'. And deleting all the caches to prevent my own tests from polluting modules that's going to be required in other tests seems to be a bit tedious. I would like them to be independent even though they are run together. Or maybe I have to use something like [rewire](https://github.com/jhnns/rewire) and let it handle that for me? Thanks! — 322896, Aug 26 '14 at 00:10

score 0 · Answer 1 · answered Mar 15 '15 at 13:32

I use node-clone to create a deep copy of a required module beforeEach test. Now the tests will use the clone instead of the cached module.

var clone = require('clone');

describe('config', function(){
  var data;

  beforeEach(function() {
    data = clone(require('./lib.js')).data;
  });

  it('should be able to add data', function() {                                         
    data.entry = 'random data';                                                         
    console.log(data);  // expecting to get `{ entry: 'random data' }`                                                                  
  })    

  it('should have empty data', function() {
    console.log(data);  // expecting to get `{}`
  })

});

If you don't use a before or beforeEach hooks you should be able to do the same across multiple files by cloning as soon as possible in each test script.

var clone = require('clone'),
data = clone(require('./lib.js')).data;

Prevent tests from polluting required modules when running Mocha for multiple test files

1 Answers1