diff --git a/.changeset/mosaic-colocate-feature-tests.md b/.changeset/mosaic-colocate-feature-tests.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/mosaic-colocate-feature-tests.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/.claude/skills/mosaic/references/testing.md b/.claude/skills/mosaic/references/testing.md
index 9431c18a6ac..d26bc1b567a 100644
--- a/.claude/skills/mosaic/references/testing.md
+++ b/.claude/skills/mosaic/references/testing.md
@@ -100,6 +100,14 @@ it('makes the selected organization active and closes', async () => {
 `packages/mosaic/src/features/user-button/__tests__/user-button.feature.test.tsx`
 is the worked example.
 
+Put a feature test next to the component it renders, and name it after that
+component. `<UserProfilePasswordSection />` is tested by
+`user-profile-password-section/user-profile-password-section.feature.test.tsx`.
+Vitest finds feature tests by the `.feature.test.tsx` suffix, so a shared
+`__tests__/` folder buys nothing and makes a section's tests harder to find.
+Existing tests in `__tests__/` folders, the worked example included, move when
+their feature next changes.
+
 ### The toolkit (`src/__tests__/feature/`)
 
 - **`fapi.ts`**: typed builders for FAPI JSON (`fapiEnvironment`, `fapiUser`,