TypeError when trying to mock Mongo DB.collection function

[Paul Karsten]

I am trying to write unit tests for an Express / Mongo app and am trying to use Sinon to mock the Mongo library so that I can test behavior without needing the database.  I am using the co module to consume the Mongo libraries use of promises.

The test listed below generates the error below:

[TypeError: db.collection is not a function]
TypeError: db.collection is not a function
    at /myApp/services/v1/project.js:76:20
    at next (native)
    at onFulfilled (/myApp/node_modules/co/index.js:65:19)

line 76 in project.js corresponds to this line "var col = db.collection('project');".

I have mocked the Db.prototype as suggested elsewhere and Db.collection is not function, but Db.prototype.collection function.


package.json

"devDependencies": {

  "mocha": "^3.0.2",

  "node-mocks-http": "^1.5.2",

  "should": "^9.0.2",

  "sinon": "^1.17.5",

  "sinon-as-promised": "^4.0.2"

},

"dependencies": {

  "body-parser": "^1.15.1",

  "co": "^4.6.0",

  "config": "^1.21.0",

  "express": "^4.14.0",

  "http-status-codes": "^1.0.6",

  "log4js": "^0.6.37",

  "method-override": "^2.3.6",

  "mongodb": "^2.2.4",

  "response-time": "^2.3.1",

  "try": "^0.13.3"

}

testProject.js

describe('Project Services Tests', function() {

  it('Test Create Project', function(done) {

    var response = buildResponse();

    var request  = HttpMocks.createRequest({

      params: {'name': UNITTESTPROJECT},

      body: {

        name: UNITTESTPROJECT,

        program: "Basic Test Data"}

    });

    var MongoMock = Sinon.mock(MongoClient);

    var DBMock = Sinon.mock(MongoClient.Db.prototype);

    var CollectionMock = Sinon.mock(MongoClient.Collection.prototype);

    var countResult = 1;

    var aResult = {result: {insertedCount: 1}};

    MongoMock.expects('connect').resolves(DBMock);

    DBMock.expects('collection').returns(CollectionMock);

    CollectionMock.expects('count').resolves(countResult);

    CollectionMock.expects('insertOne').resolves(aResult);

    response.on('end', function() {

      should(response.statusCode).equal(HttpStatus.CREATED);

      done();

    });

    project.createProjectByName(request, response);

  });

project.js:

co(function*() {

  var db = yield MongoClient.connect(dbUrl);

  var col = db.collection('project');

  var count = yield col.count({name: projectName});

  if (count > 0) {

    db.close();

    res.status(HttpStatus.FORBIDDEN);

    res.send('Project ' + projectName + ' already exists.  Duplicates not permitted');

  }

  var result = yield col.insertOne(project);

  db.close();

  if (result.insertedCount > 0) {

    res.status(HttpStatus.CREATED);

    res.send(req.protocol + '//' + req.hostname + req.originalUrl);

  } else {

    res.status(HttpStatus.INTERNAL_SERVER_ERROR);

    res.send('Project ' + projectName + ' unable to create.');

  }

}).catch(function(err) {

  res.status(HttpStatus.INTERNAL_SERVER_ERROR);

  res.send('Unable to create project' + req.params.name);

});