diff --git a/resource-timing/CodingConventions.md b/resource-timing/CodingConventions.md
index 461cae421e66c3..e8cb33a51e49a8 100644
--- a/resource-timing/CodingConventions.md
+++ b/resource-timing/CodingConventions.md
@@ -50,6 +50,11 @@ with recurring patterns.
         web performance APIs, in general).
 *   Prefer [`fetch_tests_from_window`][3] to collect test results from embedded
     iframes instead of hand-rolled `postMessage` approaches
+*   Use the [`assert_*`][4] family of functions to check conformance to the spec
+    but throw exceptions explicitly when the test itself is broken.
+    *    A failed assert indicates "the implementation doesn't conform to the
+         spec"
+    *    Other uncaught exceptions indicate "the test case itself has a bug"
 *   Where possible, we want tests to be scalable - adding another test case
     should be as simple as calling the tests with new parameters, rather than
     copying an existing test and modifying it.
@@ -57,3 +62,4 @@ with recurring patterns.
 [1]: https://www.w3.org/TR/resource-timing-2/
 [2]: https://web-platform-tests.org/writing-tests/testharness-api.html#promise-tests
 [3]: https://web-platform-tests.org/writing-tests/testharness-api.html#consolidating-tests-from-other-documents
+[4]: https://web-platform-tests.org/writing-tests/testharness-api.html#list-of-assertions