Any tips on writing testing-friendly code?

Question

Are there any guidelines for writing test-friendly Python code?

What I believe:

• One method does one thing.
• Don't use side-effects.

Any other suggestions?

Answer 1

TDD

The best tip I can give you to write test friendly code is to write the tests first. Then write the production code (TDD). Uncle Bob devised three simple rules to write TDD:

1. You are not allowed to write any production code unless it is to make a failing unit test pass.
2. You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
3. You are not allowed to write any more production code than is sufficient to pass the one failing unit test.

Especially this quote should sink in:

If you think about this you will realize that you simply cannot write very much code at all without compiling and executing something. Indeed, this is really the point.

Writing Testable Code

Also read "Writing Testable Code" from google's testing expert(are for java, but also apply to python for large parts). You should also download/read the complete PDF on that page. But a quick recap:

1. Constructor does Real Work
2. Digging into Collaborators
3. Brittle Global State & Singletons
   
4. Class Does Too Much

Answer 2

Write methods that don't rely on other models or resources - if they need to access them, they should be passed in to the method.