Express unit tests file

[z-u-a]

Hello, I have a code base of around thousands of line without unit testing. That code has multiple files including schemas, handlers, services, helpers and so on.

I need to introduce unit testing to that code base and exploring multiple file structures used in the community for organizing test cases. I am considering following approaches:

first approach, mirror of code base:

project-root/
├── src/
│ ├── handlers/
│ │ ├── handler1.js
│ │ ├── handler2.js
│ │ └── ...
│ ├── services/
│ │ ├── service1.js
│ │ ├── service2.js
│ │ └── ...
│ ├── middlewares/
│ │ ├── middleware1.js
│ │ ├── middleware2.js
│ │ └── ...
│ └── utils/
│ ├── util1.js
│ ├── util2.js
│ └── ...
├── tests/
│ ├── unit/
│ │ ├── handlers/
│ │ │ ├── handler1.test.js
│ │ │ └── handler2.test.js
│ │ ├── services/
│ │ │ ├── service1.test.js
│ │ │ └── service2.test.js
│ │ ├── middlewares/
│ │ │ ├── middleware1.test.js
│ │ │ └── middleware2.test.js
│ │ └── utils/
│ │ ├── util1.test.js
│ │ └── util2.test.js
│ ├── integration/
│ │ ├── integration1.test.js
│ │ └── integration2.test.js
│ └── e2e/
│ ├── e2e1.test.js
│ └── e2e2.test.js
├── app.js
├── package.json
└── ...

second approach: feature wise unit testing
project-root/
├── src/
│ ├── handlers/
│ │ ├── handler1.js
│ │ ├── handler2.js
│ │ └── ...
│ ├── services/
│ │ ├── service1.js
│ │ ├── service2.js
│ │ └── ...
│ ├── middlewares/
│ │ ├── middleware1.js
│ │ ├── middleware2.js
│ │ └── ...
│ └── utils/
│ ├── util1.js
│ ├── util2.js
│ └── ...
├── tests/
│ ├── login/
│ │ ├── loginHandler.test.js
│ │ ├── loginService.test.js
│ │ └── loginUtils.test.js
│ ├── registration/
│ │ ├── registrationHandler.test.js
│ │ ├── registrationService.test.js
│ │ └── registrationUtils.test.js
│ ├── common/
│ │ ├── commonUtils.test.js
│ │ └── ...
│ └── ...
├── app.js
├── package.json
└── ...

but here in express I see each SUT (system under test/funtion) in the core code is distributed in different files along with it's test cases , that's pretty new approach to me. What could be the potential pros of doing that? 1 reason I can think of is smaller the better approach. Happy to learn more. Thanks

[jonchurch]

Express is using a test file structure which is a mixture of Mirroring the file tree and splitting tests up into Features.

It's not better in any particular way, just a stylistic choice and what this package has used for a long time.

The tests aim to test specific functions, but also specific scenarios.

[z-u-a]

Thanks for the response @jonchurch