How to mock a global variable in mocha?

@domenico 

To mock a global variable in Mocha, you can use the Sinon library, which provides functionalities for creating mocks, stubs, and spies. Here is an example of how you can mock a global variable in Mocha using Sinon:

1. Install Sinon library:

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npm install sinon --save-dev

1. In your test file, import Sinon and require the module that defines the global variable you want to mock. For example, if you have a global variable named globalVar in a module named globals.js:

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const sinon = require('sinon');
const globals = require('./globals.js');

1. Use Sinon to create a mock for the global variable:

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describe('Test suite', function() {
  let globalVarMock;

  before(function() {
    globalVarMock = sinon.mock(globals, 'globalVar');
  });

  it('should test the global variable', function() {
    globalVarMock.returns('mocked value');
    // your test code here
  });

  after(function() {
    globalVarMock.restore();
  });
});

In this example, sinon.mock() is used to create a mock for the globalVar property of the globals module. You can then use the mock to set the return value for the global variable and write your test cases accordingly.

Remember to restore the mock using sinon.restore() in the after hook to clean up after the test.