Probably you have heard many advantages of unit testing such as getting bugs out of the code, producing better code design, having overall good code quality. But for me it’s all about reducing the fear of making changes in production. It gives me confidence in my code so that my new code additions didn’t break something. Also it shortens the development-testing cycle, which allows me to always publish code which works.

It’s important to distinguish unit tests from other kind of tests. If you put all kind of tests into same place it quickly can become a mess: some tests run slowly, some require testing database, a queue or other external dependency. At least in my company people don’t have a clear understanding what a unit test is and so we ended up with ice cream cone anti-pattern, where we have many end to end tests, a lot of manual testing, zero unit tests and few integration tests. Why this pattern is an anti pattern you can read in this blog post from Google testing blog.

So, what is a unit test? There are many different definitions what are the unit tests, I tend too look at them as the low-level tests, that test a single unit: function call, method, class or a group of classes. These tests should run quickly, use test stubs or mocks for external dependencies, so that they should test only the system under test and not the external dependencies. These tests are really really fast. you can run thousands of the in a second or two.

Lastly, I wanted to share some cool articles about what is and what isn’t a unit test:

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