Require is like new; An argument for DI in Node.js

As I continue my journey in Node.js I have been looking into unit testing. I typically practice TDD but while I was getting started with Node and everything was simple I was happy to play with manual testing and restarts.

I picked Mocha as a test framework. One thing I noticed quickly looking at Mocha was that the examples were simple, adding a few numbers together or checking the type of a return value.
 
Having come to Node from C# I had require littered through my code like they were using statements,  When I tried to implement some tests against the basic logic I had put together I quickly ran into a problem, that was not covered by the simple Mocha examples.  The problem arose because require is not a using statement, it directly provides code from other modules meaning that the code referenced is invoked in the tests.

I went looking for ways to mock out the require statement. As I was looking it occurred to me that mocking require is possibly not the best way to do it. In C# terms require has more in common with a static factory than a using statement.  I feel that require is not something to mock out, rather it's something to isolate.

By bringing the require statements for external modules out of the main code body the code can be broken up into a modular architecture making the system more testable and more resilient to regression issues.

Require is the best reason I have seen on my Node.js journey to include Dependency Injection in a project, even if it is a hand rolled.

Comments

Post a Comment

Popular posts from this blog

Solving `Empty reply from server` in DotNet Core

tldr; If you’re getting  curl: (52) Empty reply from server  check that you’ve configured Kestrel correctly. Long version I’ve started playing with Dotnet Core and Docker and have had a few issues getting started. I’ve had a little bit of experience with Docker, though only a little. I’ve worked with DotNet previously but never with Core. Environment The setup I’m using is a Windows laptop running Vagrant. Via Vagrant I’m running an Ubuntu Virtual Machine with the Docker run time installed. Feels a litle like inception. Key Problem The key problem that I’ve had getting started was having my Docker container not responding correctly to my curl commands. I get this: curl: (56) Recv failure: Connection reset by peer curl: (52) Empty reply from server Given that I’m not all that familliar with Docker or Dotnet Core I decided to remove one of the variables and set up a simple Express app in a different docker container. This validated that the commmand I was using to run
Read more

Testing functions that use local storage with Jest

Testing functions that use the browsers local storage API seems easy when you know how. Here's a quick run down on how to mock it out with Jest if, like me, you're not familiar with how to test it. In the end it's very little code. Consider the following TypeScript code. import { get, save, key } from "./storage"; describe(save, () => { let setItem: jest.Mock; beforeEach(() => { setItem = jest.fn(); Storage.prototype.setItem = setItem; }); it("should call set item with predefined key and json object", () => { const valueToStore = { value: "toStore" }; save(valueToStore); expect(setItem).toHaveBeenCalledWith(key, JSON.stringify(valueToStore)); }); }); The key lines are in the beforeEach call where the setItem function of the Storage prototype is assigned to an instance of jest.fn() . This allows us to make assertions on what is passed to the local storage setItem API.
Read more

Building a verify JWT function in TypeScript

# Verifying an RS232 signed JWT JSON Web Tokens (JWT) are used as a way to verify the identity of the caller of an API. **The best way to verify a JWT is to use a verification library.** I wanted to have a look at some of what those libraries are doing under the hood by putting together a function that will return if a given token is valid. In this blog I'll go through what I have done to get a validation function working. To simplify things assume: - That the signing algorithm is RS232 all others are considered invalid. - That the public keys are available on a JWKS url provided to the function eg [https://klee-test.au.auth0.com/.well-known/jwks.json](https://klee-test.au.auth0.com/.well-known/jwks.json) - I only want to know if the token was signed by a key available at the above url. I wont be checking if the token has expired, if the scopes or other claims are valid. # Break up the token A JWT is made up to 3 parts. The first thing to do in validating the token is to brea
Read more