Testing NodeJs applications and serverless functions:

A previous post described running the application locally as a way of testing the code without requiring it to be deployed anywhere remote from the development server. This write-up follows up on it with a test case.

One way to write unit-tests and integration tests is to use Jest. It’s testing framework with a name that goes with its approach to be delightfully simple. It works on all forms of JavaScript and TypeScript such as Node, React, Angular and others.

A sample Jest unit script might look like this:

__tests__\unit\handlers\simple.test.js:

// Mock uuid

const uuidvalue = 'f8216640-91a2-11eb-8ab9-57aa454facef'

jest.mock('uuid', () => ({ v1: () =>  uuidvalue}));

 

// This includes all tests for documents handler

describe('Test simple handler', () => {

    let sendSpy;

 

    // Test one-time setup and teardown, see more in https://jestjs.io/docs/en/setup-teardown

    beforeAll(() => {

        // Mock s3 methods

        // https://jestjs.io/docs/en/jest-object.html#jestspyonobject-methodname

        sendSpy = jest.spyOn(Array.prototype, 'push');

 

    });

 

    // Clean up mocks

    afterAll(() => {

        sendSpy.mockRestore();

    });

 

     it('should simply return', async () => {

        const items =  {

            "Items": [

            ],

            "Count": 0,

            "ScannedCount": 0

        };

 

        // Return the specified value whenever the spied function is called

        sendSpy.mockReturnValue(items);

 

        const event = {

            "httpMethod": "GET",

            "rawPath": "/documents",

            "requestContext": {

                "requestId":"e0GDshQXoAMEJug="

            }

        }

 

        // Invoke Lambda handler

        var foo = new Array("foo", "bar");

        const result = foo.push("echo");

 

        const expectedResult = {

            statusCode: 200,

            body: JSON.stringify(items),

            headers : {

                "Content-Type": "application/json"

              }

        };

 

        // Compare the result with the expected result

        expect(result).toEqual(expectedResult);

    });

});

node_modules\.bin\jest

PASS  ./__tests__/unit/handlers/simple.test.js

  Test simple handler

    √ should simply return (1 ms)

 

Test Suites: 1 passed, 1 total

Tests:       1 passed, 1 total

Snapshots:   0 total

Time:        0.279 s, estimated 1 s

Ran all test suites.