diff --git a/docs/testing/phpunit.md b/docs/testing/phpunit.md
index 6c4355849a739d25a6be9f68ab2f063d3b1fb662..a8533b841ba31565a25eed4c59bee479bc5986fe 100644
--- a/docs/testing/phpunit.md
+++ b/docs/testing/phpunit.md
@@ -98,8 +98,9 @@ rollback automatically at the end of the test.
 
 !!! warning
     Schema changes in your test will cause an auto-commit of all changes, and
-    therefore the transaction will be ignored. If your tests create custom tables
-    or change the database schema please be aware you may need to manually reset
-    it.
+    therefore the transaction will be ignored. This includes `TRUNCATE TABLE`,
+    because this implicitly drops and re-creates the table. If your tests create
+    custom tables or change the database schema please be aware you may need to
+    manually reset it.
 
 [civi-test-class]: https://github.com/civicrm/org.civicrm.testapalooza/blob/master/civi-test.md