How to locally test a serverless lambda function?

Question

Background

I was thrown on this project to help alleviate some stress. The trouble is no one else has done this either so I'm pioneering the cause.

What I know

I can get lambda function output locally with:

serverless invoke local -f getArticlesById -p localfile.json -s dev

and it returns a JSON article as expected.

Question

I'm using Jasmine to test my javascript lambda functions. How can I unit test these serverless environment functions locally?

Current Attempt

My lambda function is in articles/articleHandler.js. I have a test/articles.js that runs jasmine tests leveraging lambda-tester functions. Whenever I run one of these tests I get the error

TypeError: Invalid hosts config. Expected a URL, an array of urls, a host config object, or an array of host config objects.
    at new Transport (/Users/Jackson/Sites/serverless-content/node_modules/elasticsearch/src/lib/transport.js:59:13)
    at new EsApiClient (/Users/Jackson/Sites/serverless-content/node_modules/elasticsearch/src/lib/client.js:57:22)
    at Function.Client (/Users/Jackson/Sites/serverless-content/node_modules/elasticsearch/src/lib/client.js:101:10)
    at Object.<anonymous> (/Users/Jackson/Sites/serverless-content-distribution-api-v2/elasticSearch.js:6:42)
    at Module._compile (module.js:635:30)
    at Object.Module._extensions..js (module.js:646:10)
    at Module.load (module.js:554:32)
    at tryModuleLoad (module.js:497:12)
    at Function.Module._load (module.js:489:3)
    at Module.require (module.js:579:17)

I've found that this is caused by including the lambda function into the test. When I comment out that line I don't get the error. I'm guessing that because this is not a serverless call, Elasticsearch knows nothing of my environment.

test/article.js

console.log("testing articles")

const LambdaTester = require("lambda-tester");

const articleHandler = require("../articles/articleHandler.js");

describe("articles getID()", function() {
    it("test success", function() {
        return LambdaTester(articleHandler.getID)
            .event({pathParameters:{id:5633415102001}})
            .expectResult(result => {
                expect(result.body.data.id).to.be(5633415102001)
            });
    });
})
describe("articles getList()", function() {
    it("test success", function() {
        return LambdaTester(articleHandler.getList)
            .event()
            .expectResult(reset => {
                expect(result.body.data.length).to.be(10);
            });
    });
});

** ADDITIONAL **

It's looking like lambda-tester is supposed to alleviate the problem I'm encountering. Will find out more today.

Jacksonkr · Accepted Answer · 2017-11-10 16:33:39Z

3

Use lamba-tester, there are examples on the github page.

I wrote a simple lambda test function and then tested the output with jasmine + lambda-tester

As for my code, I'll need to refactor the handler someone else wrote before it will work. My simple test looks like:

Serverless yml

  testLambda:
    handler: test/testLambda.getValueOfA
    role: arn:aws:iam::367839381035:role/CodeStarWorker-fx-srch-api-v1-Lambda
    events:
      - http:
          path: test/testLambda/{a}
          method: get

Lambda Function

module.exports.getValueOfA = (event, context, callback) => {
    let a = 2;

    if(event 
        && event.pathParameters 
        && !isNaN(event.pathParameters.a)
    ) a = event.pathParameters.a;

    a = a+a;

    let ret = "the value of a is " + a;

    callback(null, ret);
}

Test

const LambdaTester = require("lambda-tester");
const TestLambda = require("./testLambda.js");

describe("testLambda()", function() {
    it("test success", function() {
        let ret;
        LambdaTester(TestLambda.getValueOfA)
            .event()
            .expectResult(result => {
                console.log(result);
                expect(result).toEqual("the value of a is 4");
            });
    });
});

I was going to set this up for parameters but didn't get there. Granted this is enough to get anyone moving forward.

answered Nov 10, 2017 at 16:33

Jacksonkr

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1 Comment

Marius B Over a year ago

I tried lambda-tester and it looks like it certainly does the job great. However, is it possible to debug the lambda functions (with setting the breakpoints in VSCode) while the lambda-tester tests are running? I couldn't find a way to do it so far, it would be the last piece of the puzzle from my point of view.

vgaltes · Accepted Answer · 2018-10-11 12:39:17Z

0

another option you have is to call the function directly from your test. In the end, it's nothing more than a function, so you can import the module and call it, passing the right parameters.

answered Oct 11, 2018 at 12:39

vgaltes

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