On 100% Coverage

Yes, we need to write tests because it is something that we think will help us in the long term, even though it may be more work for us in the short run. If written with care and with the end in mind, tests serve as living documentation, living because they change as much as the application code changes, and they help us refer back to what some feature does and doesn’t, in as much detail as we want. Tests let us know which areas of the application matters to us, and every time they run they remind us of where our bearings currently are.

Tests may be user journeys in the user interface, a simulation of requests and response through the app’s API, or small tests within the application’s discrete units, most likely a combination of all these types of tests, perhaps more. What matters is that we find some value in whatever test we write, and that value merits its cost of writing and maintenance. What’s important is asking ourselves whether the test is actually significant enough to add to the test suite.

It is valuable to build a good enough suite of tests. It makes sense to add more tests as we find more key scenarios to exercise. It also makes sense to remove tests that were necessary in the past but aren’t anymore. However, I don’t think it is particularly helpful to advocate for 100% test coverage, because that brings the focus on a numbers game, similar to how measuring likes or stars isn’t really the point. I believe it is better when we discuss among ourselves, in the context we’re in, which tests are relevant and which are just diving into minutiae. If our test suite helps us deploy our apps with confidence, if our tests allows us to be effective in the performance of our testing, if we are continuously able to serve our customers as best as we can, then the numbers really doesn’t amount to much.

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