我该如何在被测试的类/方法中加载的对象中添加方法？

Question

Our MEANJS application has a class (Eg, CompanyService ) that loads an object (Eg, CompanyRepo ) of another class and calls a method on it. I am trying to write unit tests for the CompanyService class and would need to stub a method in the CompanyRepo method to simulate a promise rejection. However, despite the stub, the CompanyService method call seems to call the actual CompanyRepo method call.

The code flow is as below,

companyService method

function isDomainExists(domain) {
    return new Promise(function(resolve, reject) {
        companyRepo.getCompanyByDomain(domain)
                .then(function (company) {
                    return resolve(company);
                }, function(rejected) {
                    return reject("Error");
                })
    } });

Unit test method

var stub = sinon.stub(companyRepo,"getCompanyByDomain").rejects("error"); it('Should return company not registered if there is a DB error', function() {
    return companyService.isDomainExists("test company").should.eventually.be.rejected(); }); stub.restore();

Output

Company service isDomainExists method Should return company not registered if there is a DB error: AssertionError: expected promise to be rejected but it was fulfilled with { Object ($__, isNew, ...) }

I think I can understand what is happening here. The companyService class has a require statement that loads the companyRepo class which gets executed even before the stubbing happens. Is there any method by which I can avoid this from happening? What is the recommended best practice in this case?

Answer 1

I couldn't get it to work properly with should, but did get this to work, see if it helps:

companyService:

var companyRepo = require('./companyRepo');

function isDomainExists(domain) {
    return new Promise(function (resolve, reject) {
        companyRepo.getCompanyByDomain(domain)
            .then(function (company) {
                console.log('----in main resolve')
                return resolve(company);
            }, function (rejected) {
                console.log('----in error catch')
                // return reject(new Error('Errorx'));
                return reject('Error');
            });
    });
};

exports.isDomainExists = isDomainExists;

companyRepo

exports.getCompanyByDomain = () => { 
    console.log('-----in real getCompanyByDomain');

    return Promise.resolve('resolve from real function');
}

Test

it('Should return company not registered if there is a DB error', async function () {
    var stub = sinon.stub(companyRepo, "getCompanyByDomain").rejects("fake_error");

    await expect(companyService.isDomainExists("test company")).to.eventually.be.rejectedWith('Error');

    stub.restore();
});

It is rejecting with Error (and not fake_error) because your reject function sends 'Error' regardless.

Should sometimes acts funny, no idea why, also, try moving stub / resotre inside the test (or in beforeEach, afterEach).

There was also a small typo in companyRepo definition.

If nothing else works (i've seen this in some cases), try rewire to stub instead:

var rewire = require('rewire')
//notice not using require here
var companyService = rewire('./companyService');

it('should stub', async () => {
    let fake = {
        getCompanyByDomain: () => {
            console.log('------rewired stub')
            return Promise.reject('rewired_error');
        }
    }

    companyService.__set__('companyRepo', fake);

    await expect(companyService.isDomainExists("test company")).to.eventually.be.rejectedWith('Error');
    //reset
    companyService = rewire('./companyService');
});