Test example using Dject

dject-test-example.js

'use strict';

const assert = require('chai').assert;
const sinon = require('sinon');
const container = require('../example-container');

describe('file reader', function () {
    let fileReader;
    let logSpy;
    
    beforeEach(function () {
        // Building test doubles for node internals becomes trivial
        const fsFake = {
            readFileSync: () => throw new Error('The error is coming from inside the test!')
        };
        
        logSpy = sinon.spy();
        const loggerFake = {
            log: logSpy
        };
        
        // Create a child container to isolate the tests from your main container so you don't contaminate other tests.
        const childContainer = container.new();
        
        // This gives us direct line-of-sight into what our test doubles will be doing
        // Since there is no filesystem or module caching, moving dependencies won't
        // impact our test isolation
        childContainer.register(() => fsFake, 'fs');
        childContainer.register(() => loggerFake, 'logger');
        
        // Note, this file can be moved without impacting the tests.
        fileReader = childContainer.build('fileReader');
    });
    
    describe('readAFile', function () {
        
        it('logs an error when the filesystem cannot read a file', function () {
            fileReader.readAFile('./some/test/file.txt');
            assert.equal(logSpy.getCall(0)[0], 'The error is coming from inside the test!');
        });
        
    });
});