diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e40f0b4..c56b55b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -45,6 +45,8 @@ Automatically fix most linting issues:
 
 ## Testing
 
+Testing requires running Mastodon itself, meaning the [Mastodon development guide](https://github.com/tootsuite/documentation/blob/master/Running-Mastodon/Development-guide.md) is relevant here. In particular, you'll need a recent version of Ruby, Redis, and Postgres running.
+
 Run integration tests, using headless Chrome by default:
 
     npm test
@@ -87,4 +89,4 @@ Tests use [TestCafé](https://devexpress.github.io/testcafe/). The tests have a
 * `1xx-test-name.js`: tests that do modify the Mastodon database
 
 In principle the `0-` tests don't have to worry about
-clobbering each other, whereas the `1-` ones do.
\ No newline at end of file
+clobbering each other, whereas the `1-` ones do.