Testing is the art of delegating the mental load to the machine in order to:

• Have a quicker feedback loop
• Design your code
• Refactor safely
• Document the codebase

When you have a tested codebase you put yourself and your team on the road to success: everyone works in a safe environment backed up by "security nets".

But... what should we test ?

In this article I will break down the 4 kinds of tests you can do in Flutter.

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You can find the implementation of each kind of test in this Github repository:

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Unit tests

I think people fails at Unit tests because they focus on implementation details rather than focusing on business value of the application: the use-cases.

Unit tests gather the following characteristics:

• Runs in-memory (< x0 ms)
• Spot functional regression
• Involves Use-cases and Domain layers
• Uses a fake Infrastructure

Use-cases are all the reads and writes of your application:

• Signup with credentials
• Signin with Google
• Retrieve current progression
• Save workout program
• etc.

You can find an example here.

Smoke tests

"Pschhhh" - a smoke test running.

Also known as Widget tests, they are focus on user interactions with the UI.

I like to write them with a BDD-style:

• Given an unknown user on the Signup page, When he enters a badly formatted email, Then he should see an error message.
• Given a well-known user on the Login page, When he enters his credentials in the login page, Then he should be redirected to the Home page.
• etc.

These tests has the following characteristics:

• Runs in-memory (< x00 ms)
• Spot functional regression
• Involves UI, Use-cases and Domain layers
• Uses a fake Infrastructure

If you struggle to achieve the desired assertion, you may have a problem on one of your use-case: then, you can fallback to your unit tests :) !

You can find an example here

Snapshots tests

Known as "Golden tests", focused on the UI, they spot Visual regressions:

• Runs in-memory (< x00 ms)
• Spot visual regressions
• Involves UI

E2E tests

Similarly to smoke tests, they are focus on the user interactions with the UI but they involves the real infrastructure implementation and runs on a device:

• Runs on a device ( < x000 ms)
• Spot functional regression
• Involves UI, Uses-cases, Domain, Infrastructure

If you have used a BDD-style approach for your smoke tests with reusable steps, you should be able to write meaningful e2e tests in no-time :)

You can find an example here

Wrap up

If you have this 4 kinds of test in your codebase, congratulations, you are sure to have one of the strongest test suite possible with Flutter !