An introduction to Unit Tests (UT), Mocks, Integration Tests (IT), End-to-end Tests (E2E).

Say that you want to learn how to drive. πŸš—

At home, you have a car simulator.
Your Unit Tests will be:
πŸ”Έhow to turn on the car
πŸ”Έhow to speed up
πŸ”Έhow to slow down
πŸ”Έwhat to do with a red light

You are not using a real car, but a simulator. This is your *mock*.

UTs: test the behaviors in a controlled environment with mocks.

They are fast: you can stay at home with your simulator. In a minute you'll be able to redo your tests and add more (eg: turn on the lights)

Now it's time to try a real car, in a parking lot. πŸ…Ώ

Do the same actions you've seen work with a real car?

Those are Integration Tests: use real stuff, do better tests;

ITs are slower than UTs - you need a real environment, with a parking lot and a real car

What more do ITs add that you can't find with UTs?
For example, that the simulator used a car with automatic shift, but the real car has manual shift.

Or that you have to turn on the car before accelerating.

The actions you've tried with UT were all correct if performed in a "sandbox"! With ITs you put those tests together, into the real world.

But you're still in a parking lot.

With E2Es you put everything in practice, but this time for real.
Use a real car, on a real road, with real semaphores and other factors (traffic jams, blocked roads...)

E2Es are way slower than UTs, but provide you more info about a real scenario.

You will not run them for every new small thing you learn about driving. But you focus on a real scenario (eg: go to the nearest Walmart)

All those kinds of tests are useful in different ways. UTs are faster but in a sandboxed env. E2Es are slower but focused on real scenarios.

🐒Slow ⚑Fast
🌎Wide πŸ—œNarrow


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