MochaJS + SinonJS + Promises

Example-Mocha-Sinon-Promises.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 JsonZipper = require('../JsonZipper');

describe('JsonZipper', function() {

  afterEach(function() {
    fs.readdirSync.restore();
    fs.readFileSync.restore();
    fs.writeFileSync.restore();
  });

  it('can zip files', function() {
    const fsReadDir = sinon.stub(fs, 'readdirSync').returns([ 'file.json' ]);
    const fsReadFile = sinon.stub(fs, 'readFileSync').returns( '{}');
    const fsWriteFile = sinon.stub(fs, 'writeFileSync');

    const jz = new JsonZipper('./');    
    return jz.zipJsonFiles()
      .then(function() {
        assert(fsReadDir.called);
        assert(fsReadFile.called);
        assert(fsReadFile.calledAfter(fsReadDir));
        assert(fsWriteFile.called);
        assert(fsWriteFile.calledAfter(fsReadFile));
      });
  });

  it('can zip 2 files', function() {
    const fsReadDir = sinon.stub(fs, 'readdirSync').returns([ 'file.json', 'file2.json' ]);
    const fsReadFile = sinon.stub(fs, 'readFileSync').returns( '{}');
    const fsWriteFile = sinon.stub(fs, 'writeFileSync');

    const jz = new JsonZipper('./');    
    return jz.zipJsonFiles()
      .then(function() {
        assert(fsReadDir.called);
        assert(fsReadFile.called);
        assert(fsReadFile.calledAfter(fsReadDir));
        assert(fsWriteFile.called);
        assert(fsWriteFile.calledAfter(fsReadFile));
      });
  });
});