e8f91696fe
End-to-end tests using the `jj` binary are often easy and natural to write, but it's easy to miss how much slower they are than `jj-lib` tests.
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Prefer lower-level tests to end-to-end tests
When possible, prefer lower-level tests that don't use the jj binary.
End-to-end tests are much slower than similar tests that create a repo using
jj-lib (roughly 100x slower). It's also often easier to test edge cases in
lower-level tests.
It can still be useful to add a test case or two to check that the lower-level
functionality is correctly hooked up in the CLI. For example, the end-to-end
tests for jj log don't need to test that all kinds of revsets are evaluated
correctly (we have tests in jj-lib for that), but they should check that the
-r flag is respected.
Use end-to-end tests for testing the CLI commands themselves.