diff --git a/.agents/skills/usethis-python-code-modify/SKILL.md b/.agents/skills/usethis-python-code-modify/SKILL.md
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+---
+name: usethis-python-code-modify
+description: Modify Python code (e.g. refactor, add new code, or delete code)
+compatibility: usethis, Python, pytest
+license: MIT
+metadata:
+  version: "1.0"
+---
+
+# Modifying Python code
+
+## Procedure
+
+1. Run a subset of the tests for `src/<module>` regularly from the parallel module in the `tests/<module>` directory. Never run the entire test suite.
+2. After finishing your modifications, run the static checks (e.g. `usethis-qa-static-checks`) to check for any issues.
+
+## Run a subset of tests regularly
+
+When modifying Python code, regularly run a relevant subset of the tests. The test suite is structured such that there are tests for each module in the `src` directory in the `tests` directory. For example, if we had `src/usethis/_a.py`, we would have `tests/test_a.py` with tests for that module.
+
+### Never run the entire test suite
+
+Running the entire test suite is unusually unnecessary and it is slow. The CI will run the entire test suite, so it is unnecessary for you to do so.
+
+### What to do when tests fail
+
+There are two reasons why tests might fail:
+
+- The tests' expectations are no longer correct (e.g. because you changed the behavior of the code)
+- There is a bug in the code
+
+In the first case, update the tests to have the correct expectations, or perhaps remove the test entirely. In the second case, fix the bug in the code.
+
+## Run static checks after finishing modifications
+
+After finishing your modifications, run the static checks (e.g. `usethis-qa-static-checks`) to check for any issues before merging.
diff --git a/.agents/skills/usethis-python-module-layout-modify/SKILL.md b/.agents/skills/usethis-python-module-layout-modify/SKILL.md
index a8165f1a..609da098 100644
--- a/.agents/skills/usethis-python-module-layout-modify/SKILL.md
+++ b/.agents/skills/usethis-python-module-layout-modify/SKILL.md
@@ -1,7 +1,7 @@
 ---
 name: usethis-python-module-layout-modify
 description: Modify the Python module layout (create, move, rename, or delete modules)
-compatibility: usethis, Python
+compatibility: usethis, Python, pytest
 license: MIT
 metadata:
   version: "1.2"