Testing the creation of a new document ID using mocks in a cloud function unit

Question

Testing the creation of a new document ID using mocks in a cloud function unit

When it comes to Firestore cloud function TypeScript unit tests, my focus is on mocking doc().id, while leaving doc('path') untouched. Can anyone suggest how I can achieve this?

admin.firestore().collection('posts').doc().id // Mocking only this line

admin.firestore().collection('posts').doc('1')

I attempted the following approach using sinon, but encountered an infinite loop issue at sinon/proxy-invoke.js:50:47:

const collection = admin.firestore().collection('posts');
sinon.stub(collection, 'doc').callsFake(path => 
   path === undefined ? mock : collection.doc(path)
);
sinon.stub(admin.firestore(), 'collection')
  .callThrough()
  .withArgs('posts')
  .returns(collection)

Another attempt involved the following code, however, the doc(documentPath: string) method ended up being stubbed out as well:

sinon.stub(collection, 'doc')
  //@ts-ignore
  .withArgs()
  .returns(mock)

If there's a workaround available in other mock libraries, I'm open to exploring those options.

typescript google-cloud-firestore google-cloud-functions sinon

Answer 1

Answer №1

Encountering an infinite loop is a common issue when you recursively call the stubbed method in your code:

sinon.stub(collection, 'doc').callsFake(path => 
   path === undefined ? mock : collection.doc(path) // <- this calls the stub again
);

To resolve this problem, it is crucial to extract the original doc method from the object being stubbed. Moreover, utilizing the standard function syntax ensures that the context of this is correctly passed to the fake callback (and any other functions being invoked). Even though the doc function presently accepts only one path argument, incorporating rest parameters is recommended for comprehensive argument handling.

// Retain the untouched function (ensure this is executed just once
// to avoid storing a stubbed function)
const _originalDoc = collection.doc;

sinon.stub(collection, 'doc')
  .callsFake(function (...args) { // critical! Employ `function`, not arrow function
    // The context of `this` within this function is a CollectionReference instance
    return args.length = 0 || args[0] === undefined // don't overlook the return statement
      ? mock.call(this)                // invoke the mocked function
      : _originalDoc.apply(this, args) // trigger the original function with its initial arguments
  });

In case your mock includes invocations of collection.doc(), ensure that the authentic function is called rather than the stubbed version (unless deliberately intended).

Answer 2

Encountering an infinite loop is a common issue when you recursively call the stubbed method in your code:

sinon.stub(collection, 'doc').callsFake(path => 
   path === undefined ? mock : collection.doc(path) // <- this calls the stub again
);

To resolve this problem, it is crucial to extract the original doc method from the object being stubbed. Moreover, utilizing the standard function syntax ensures that the context of this is correctly passed to the fake callback (and any other functions being invoked). Even though the doc function presently accepts only one path argument, incorporating rest parameters is recommended for comprehensive argument handling.

// Retain the untouched function (ensure this is executed just once
// to avoid storing a stubbed function)
const _originalDoc = collection.doc;

sinon.stub(collection, 'doc')
  .callsFake(function (...args) { // critical! Employ `function`, not arrow function
    // The context of `this` within this function is a CollectionReference instance
    return args.length = 0 || args[0] === undefined // don't overlook the return statement
      ? mock.call(this)                // invoke the mocked function
      : _originalDoc.apply(this, args) // trigger the original function with its initial arguments
  });

In case your mock includes invocations of collection.doc(), ensure that the authentic function is called rather than the stubbed version (unless deliberately intended).

Testing the creation of a new document ID using mocks in a cloud function unit

Answer №1

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