diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d0dcfcf8..11f14608 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -8,4 +8,8 @@ This document builds on the [default contributing.md](https://github.com/comcode
 
 ## How to make changes to code
 
+### Creating tests
+
+Test files must be within `/src`, with a file name ending in `.test.<ext>`, where `<ext>` is one of `js` `mjs` `jsx` `ts` `tsx`.
+
 ## How to review a code change
diff --git a/jest.config.js b/jest.config.js
index 8eb2a6ac..27df1631 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -2,8 +2,6 @@
 module.exports = {
   preset: "ts-jest/presets/js-with-ts-esm",
   testEnvironment: "node",
-  testMatch: [
-    "**/__tests__/**/*.{[jt]s?(x),mjs}",
-    "**/*(*.)+(spec|test).{[jt]s?(x),mjs}",
-  ],
+  // tests must be within /src, with .spec or .test before file extension
+  testMatch: ["<rootDir>/src/**/*(*.)+(spec|test).{[jt]s?(x),mjs}"],
 };