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

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

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 usin...
Read more

Can't resolve DNS Aws

Image
I recently registered a domain for a joke website  saladsimulator.com .  I figured I could whip up the page in a couple of minutes and throw it up on AWS using S3 static site hosting.  All done in an hour or so. What I thought would take an hour ended up in a multi-day ordeal while I tried to get the DNS to resolve.  I went through what seem to be the typical problems. The bucket wasn't configured to be accessible as a website. My bucket wasn't named the same as the website; the bucket needed to be saladsimulator.com to match the domain saladsimulator.com . I got these fixed up and found that it still wasn't working.  I added extra routes in to see if I could Alias or CNAME to a known working site, but they didn't work either. So it seemed it was a problem with something to do with the DNS configuration. After searching around I found a mention in a thread that the name server records in the hosted zone needed to match those in the domain name registrat...
Read more