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Comment by enos_feedler | Hacker News Reader

Why do we have to choose one or the other? Its ridiculous to stack these test methodologies against each other. You need both for different reasons. Unit tests verify the function of a unit. System-level tests verify the integration of units with other units. Instead of writing an exhaustive list of both, you learn over time the kinds of tests you need for each scenario.

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I tend to agree - but if I could redraw that triangle it would be more like a trapezium. Not enough emphasis is given to system tests - and it shows in the tooling and the community mentality.

On my current project no one would dream of adding a new feature without unit tests - but everyone turns a blind eye to integration and system tests because "they're hard".

That's the point of the testing pyramid at the end of the article. My rule of thumb is this: if you can test something at the unit testing level with mocks and feel confident about the behavior then do so. Otherwise, start moving up the pyramid (isolated integration tests > end of end integration tests > UI tests).

The higher you get the more time it takes for tests to run, the more difficult it is to identify where a failure is, the more brittle those tests will be because of inter-dependencies, and the more complex it is to write the test. The difficult part is understanding your system well enough to know where your unit tests aren't sufficient.

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