Unit test for aws lambda using jest - node.js

Question

const invokeApi = require("/opt/nodejs/kiwiCall");
const decrypt = require("/opt/nodejs/encryption");
const cors = require("/opt/nodejs/cors");
When I am testing my index.js file by manual mocking these dependencies in mocks directory as follows:
__mocks__
|_invokeApi
|_decrypt
|_cors
it says
FAIL ./index.test.js
● Test suite failed to run
Cannot find module '/opt/nodejs/kiwiCall' from 'index.js'
However, Jest was able to find:
'../../../../lambdas/Flights/Locations/index.js'
You might want to include a file extension in your import, or update your 'moduleFileExtensions', which is currently ['js', 'json', 'jsx', 'ts', 'tsx', 'node'].
See https://jestjs.io/docs/en/configuration#modulefileextensions-array-string
1 | "use strict";
2 |
> 3 | const invokeApi = require("/opt/nodejs/kiwiCall");
Wanted to know how can I mock the dependencies of AWS lambda in inedx.test.js file

Answer 1

In your package.json or jest.config you could add a moduleNameMapper for that directory.
"jest": {
"moduleNameMapper": {
"/opt/nodejs/(.*)": "<rootDir>/../nodejs/$1"
},
},

Answer 2

So I managed to figure out something based on my repository.
I'm using the moduleNameMapper to map the absolute path to another location in my repository to where I have the layer stored.
Eg.
moduleNameMapper: {'^/opt/config/config': '<rootDir>/src/layers/layers-core/config/config'}
In your case you could use a regex expression to match /opt/nodejs/ and map it elsewhere. Hope that helped.
EDIT:
I completely changed my approach and used babel-plugin-module-resolver with babel-rewire. I did this because the above method was incompatible with rewire. It's quite easy setup and you just need to setup a babel alias within .babelrc.
eg.
{
"plugins": [
["rewire"],
["babel-plugin-module-resolver", {
"alias": {
"/opt/config/config": "./src/layers/layers-core/config/config",
"/opt/utils/util-logger": "./src/layers/layers-core/utils/util-logger",
"/opt/slack": "./src/layers/layers-slack/slack"
}
}]
]
}
Combine this with IDE jsconfig.json path alias and you get full IDE support.
{
"compilerOptions": {
"module": "commonjs",
"target": "es2018",
"baseUrl": "./",
"paths": {
"/opt/config/config": ["src/layers/layers-core/config/config"],
"/opt/utils/util-logger": ["src/layers/layers-core/utils/util-logger"],
"/opt/slack/*": ["src/layers/layers-slack/slack/*"],
}
},
"exclude": ["node_modules", "dist"]
}
You can then reference your layers with jest.doMock('/opt/config/config', mockConfig);
EDIT 2:
Found a way to get Jest to mock it. Just slip {virtual: true} into the mock!
jest.doMock('/opt/config/config', mockConfig, {virtual: true});

Answer 3

I have pretty much the same issue. I have defined a layer which contains common code that's shared between other functions in my project. My project structure looks something like this:
project/
functions/
function1/
app.js
function2/
app.js
shared/
shared.js
I import my shared library like this:
const { doSomething } = require('/opt/shared');
exports.handler = async (event) => {
const result = await doSomething();
// etc...
return {statusCode: 200};
}
This works when I deploy to AWS Lambda because the /opt/shared exists and it can be referenced correctly. It also works if I run this on my machine using sam local invoke Function1 because it's running in a container, which makes /opt/shared available to the code.
However, I'm struggling to work out how I can mock this dependency in a unit test. If I simply do this: jest.mock('/opt/shared'), I'm getting: Cannot find module '/opt/shared' from app.test.js

Answer 4

You can use the modulePaths option, from this post.
Documentation
jest.config.js
"jest": {
"modulePaths": [
"<rootDir>/src/layers/base/nodejs/node_modules/"
]
}
You can dynamically create this array by scanning a directory
const testFolder = './functions/';
const fs = require('fs');
const modulePaths = fs.readdirSync(testFolder)
.reduce((modulePaths, dirName) => {
modulePaths.push(`functions/${dirName}/dependencies/nodejs/node_modules/`);
return modulePaths;
}, []);