MochaJS, SinonJS, Proxyquire, and how to stub internally instantiated classes

Example-Mocha-Sinon-Promise-Proxyquire.js

'use strict';

const fs = require('fs');
const path = require('path');
const NodeZip = require('node-zip');

class JsonZipper {
  constructor(path) {
    this.path = path;
  }

  zipJsonFiles() {
    const self = this;
    return new Promise( function(resolve, reject) {
      const files = fs.readdirSync(self.path);
      const zippedFiles = [];
      for (let i = 0; i < files.length; i++) {
        const file = files[i];

        if (file.endsWith('.json')) {
          const fullPath = path.join(self.path, file);
          const zipFullPath =  fullPath + '.zip';
    
          const zip = new NodeZip();
          zip.file(file, fs.readFileSync(fullPath));
          const data = zip.generate({ base64: false, compression: 'DEFLATE' });
          fs.writeFileSync(zipFullPath, data, 'binary');
          zippedFiles.push(zipFullPath);
        }
      }

      resolve(zippedFiles);
    });
  }
}

module.exports = JsonZipper;

test.js

'use strict';

const assert = require('assert');
const fs = require('fs');
const sinon = require('sinon');
const proxyquire = require('proxyquire');

let zipFileStub, zipGenerateStub;
let fsReadDir, fsReadFile, fsWriteFile;
let jsonZipperStub;

describe('JsonZipper', function() {

  beforeEach(function() {
    

    zipFileStub = sinon.stub();
    zipGenerateStub = sinon.stub();
    fsReadDir = sinon.stub();
    fsReadFile = sinon.stub();
    fsWriteFile = sinon.stub();

    function MockNodeZip() {
      MockNodeZip.prototype.file = zipFileStub;
      MockNodeZip.prototype.generate = zipGenerateStub;
    }

    jsonZipperStub = proxyquire('../JsonZipper', {
      'node-zip': MockNodeZip, // needs to be what goes through require
      fs: {
        readdirSync: fsReadDir,
        readFileSync: fsReadFile,
        writeFileSync: fsWriteFile,
      }
    });
  });

  it('fails when NodeZip fails', function(done) {

    fsReadDir.returns(['file1.json']);
    fsReadFile.returns('{}');
    zipGenerateStub.throws();

    const jz = new jsonZipperStub('./somewhere');    
    jz.zipJsonFiles()
      .catch(function(err) {
        assert.ok(true);
      })
      .then(done);
  });

  it('can zip files', function() {

    fsReadDir.returns(['file1.json']);
    fsReadFile.returns('{}');


    const jz = new jsonZipperStub('./somewhere');    
    return jz.zipJsonFiles()
      .then(function() {
        assert.equal(fsReadDir.callCount, 1);
        assert.equal(fsReadFile.callCount, 1);
        assert.equal(fsWriteFile.callCount, 1);
        assert.equal(zipGenerateStub.callCount, 1);
      });
  });

  it('can zip 2 files', function() {
    fsReadDir.returns([ 'file.json', 'file2.json' ]);
    fsReadFile.returns( '{}');

    const jz = new jsonZipperStub('./somewhere');    
    return jz.zipJsonFiles()
      .then(function() {
        assert.equal(fsReadDir.callCount, 1);
        assert.equal(fsReadFile.callCount, 2);
        assert.equal(fsWriteFile.callCount, 2);
        assert.equal(zipGenerateStub.callCount, 2);

      });
  });

  it('gracefully does not zip zero files', function() {
    fsReadDir.returns([ ]);
    fsReadFile.throws();

    const jz = new jsonZipperStub('./somewhere');    
    return jz.zipJsonFiles()
      .then(function() {
        assert.equal(fsReadDir.callCount, 1);
        assert.equal(fsReadFile.callCount, 0);
        assert.equal(fsWriteFile.callCount, 0);
      });
  });
});