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... or, what kind of regression tests should City of Helsinki services have?
well-tested program - adapting to every change - no surprises here! -- Panu Kalliokoski, programming haikus
- integration tests that cover the happy paths of each feature and user
- this means a program that does what the user would do (against a real service) and checks that what happens is what should happen
- integration or unit tests that cover forbidden behavior
- a program that does what a hacker would do and checks that it fails
- unit tests for every method/function whose logic is "complicated"
- "complicated" means there are at least three execution paths in the method/function
- integration or unit tests that provide full code coverage at least for
all code that implements the running service
- this is meant to exclude build-time helper scripts and similar stuff. But consider testing them, too!
- at least rudimentary performance tests: how long does it take to load
each view 1000 times?
- these produce an important time series where you can find when you made a performance blunder
- randomised fuzz testing to see that the service doesn't break (or reports errors correctly)
- state invariants if your data has interdependencies
- these can be made on database level
- Prefer integration (and e2e) tests over unit tests.
- Use unit tests for stuff that is hard to understand even on a local (unit) level.
- Integration tests are good for covering a lot of stuff quickly. Unit tests are good for finding exactly where a problem is.
- Don't use mocks unless it simplifies tests considerably. That is,
don't redo software components in a simplified way.
- instead, use the real components for tests, too.
- if the real component is really hard to use, then a mock (or fake version) might be feasible. Consider fixing the real component, though.
- Don't overtest or undertest. (This is hard.)
- Undertesting means that broken things go unnoticed. Write enough tests to cover all execution paths and test the results are right from the unit/service user's point of view.
- Overtesting means that change is hard because most of the time goes into fixing tests. In the test, don't check for details that are irrelevant and might change.
- Use fixtures (such as prepopulated data in the database) if your tests
- However, don't make your tests depend very much on the detail of testing data. Testing data will inevitably have to be updated someday.
- Build stateless services if you can. Put state into specialised
stateful services (buckets, databases).
- This way, the state can always be initialised (by fixtures) so that tests work predictably.
- Use stateless handlers (pure functions/components) wherever you can.
- Model your program as functions that process input data into output data. Hoist all I/O and other interaction onto as high level in the program as possible.
- In UI programs, separate state handling from the rest of the program.
- You can test your reducers (state update functions) separately if they are "complicated".