Writing tests as specification

Tests are the best form of specification because:

  • Tests can be run, which means you can programmatically verify your implementation against your specification. If the tests pass, your implementation conforms to the specification.
  • Tests are an integral part of the code (that is, Specification-as-Code (SaC)). There is less chance that your specification becomes outdated, because if it does, the test would fail.

Therefore, we can write our technical specifications as E2E tests, which then drives the TDD development process.

Remember that it's very hard for a single developer to be able to conjure up an exhaustive list of scenarios and edge cases to test for; we are bound to miss some. That's why it is important that the tests and code are inspected by multiple people. This may involve w riting the test descriptions as a pair or mob, putting in place a c ode review workflow involving developers both within and outside the project. Doing so maximizes the value of the tests and ensures that they cover the most relevant edge cases.
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