How to unit-test a AWS Lambda use lambda-local with mocha? - unit-testing

Question

Background
I am working on a project that is build with Serverless framework with serverless-appsync-plugin. I implemented a single endpoint(AWS Lambda) to handle all the requests generate from Appsync through graphQL. The endpoint will route the request to the corresponding function to perform the operation.
Problem
Now that I have developed around 10+ operations, I want to automate the process of unit-testing. For simplicity, I decided to run that single endpoint as a lambda locally for all the testing (against running appsync-offline).
So, I used lambda-local with mocha. However, I am not able to get a test-case to fail, based on the response I got from the lambda.
it('db should have a user of uId: 123', async function () {
lambdaLocal.execute({
event: makeUserEvent({userId: '123'}),
callbackWaitsForEmptyEventLoop: false,
lambdaPath,
callback: function(err, data) {
if(err) {
console.log(1)
expect.fail(null, null, 'You are not supposed to be here') //should fail here
} else {
console.log(2)
// some checking here, may fail or may not fail
expect.fail(null, null, 'return fail if the userId is 234') //should fail here too
}
}
});
console.log(3)
})
In both of the situation I want it to fail, it is not failing the test cases for either callback('failed', null) or callback(null, 'success').
So, what is the right way to make the lambda-local to fail a test case?

Answer 1

In your code the test finishes without mocha registering that the assertions in lambdaLocal.execute failed. So it will always pass.
Instead of using the callback parameter you could return a promise, or await the lambdalocal.execute and then do your assertions.
For example (using Promises):
it('db should have a user of uId: 123', function () {
return lambdaLocal.execute({
event: makeUserEvent({userId: '123'}),
callbackWaitsForEmptyEventLoop: false,
lambdaPath })
.then(
(data) => {
console.log(2)
// some checking here, may fail or may not fail
expect.fail(null, null, 'return fail if the userId is 234') //should fail here
},
(err) => {
console.log(1)
expect.fail(null, null, 'You are not supposed to be here') //should fail here
})
}
Alternatively change signature of the function that is passed to it to take an additional parameter (usually called done) which will then be used by mocha to pass a function that can be used to signalise that the test finished. See the mocha documentation for more info.