Unit Testing Tenets
===================

Tres Seaver's unit testing tenets.

Goals
-----

Unit tests should:

- be as simple as possible while still exercising the app under test.

- run as quickly as possible to encourage running them frequently.

- avoid couplings with other tests, or with parts of the codebase they are not
  responsible for testing.

- be idempotent.

Tests should not:

- replace narrative or API documentation.

Rules
-----

- Never import the module under test at test module scope.

- Each test case method tests Just One Thing.

- Test case names indicate what they test.

- Don't share test fixtures between test modules.

Guidelines
----------

- Minimize module-scope dependencies.

- Do as little work as possible in the execution path of a single test.

- Make fixtures as simple as possible.

- Use globals judiciously.

- Use stub/mock objects to clarify dependent contracts.

Conclusions
-----------

- Tests are straightforward to write.

- Excellent coverage.

- Easy to debug/diagnose.

- Quick to run.

- Clarifies thinking about the code and its dependencies.

Demonstration
-------------

Let's go back and improve the tests we wrote using Tres' tenets.

What Do We Want To Fix
++++++++++++++++++++++

- Bad test practices (importing things under-test at module scope).

- Bad/missing stubs or mocks.

- Bad fixtures.

- Misuse of globals.

API Talk (Tangent)
+++++++++++++++++++

- Avoid Global State When Possible

- Avoid Designing for Convenience (Don't Give In To ``import`` Fascination)

- Composition Usually Beats Inheritance

- Avoid Using Others' Code That Breaks These Rules