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

Question

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

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!

javascript
node.js
testing
mocha
require

Answer 1

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;