input.
- In a test file, put constants immediately after the imports, then the
tests, then supporting types, methods, and helpers.
+- Keep a helper that only one test file uses in that file. Put a helper
+ that more than one test file uses in a file without tests. Name that
+ file for what it holds, and end the name with `_helper_test.go`.
- Supply valid required dependencies in tests. Do not make a dependency
optional only to make a test simpler.