Style guide

Panics

Panics are not allowed, especially in code that may run on a server. Calling .unwrap() is okay if it's guaranteed to be safe by previous checks or documented invariants. For example, if a function is documented as requiring a non-empty slice as input, it's fine to call slice[0] and panic.

Markdown

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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.