diff --git a/docs/en/02_Developer_Guides/06_Testing/00_Unit_Testing.md b/docs/en/02_Developer_Guides/06_Testing/00_Unit_Testing.md
index 7afd1894c..098b5e3d1 100644
--- a/docs/en/02_Developer_Guides/06_Testing/00_Unit_Testing.md
+++ b/docs/en/02_Developer_Guides/06_Testing/00_Unit_Testing.md
@@ -73,6 +73,10 @@ The `phpunit` binary should be used from the root directory of your website.
 	phpunit framework/tests '' flush=all
 	# Run tests with optional `$_GET` parameters (you need an empty second argument)
 
+<div class="alert" markdown="1">
+The manifest is not flushed when running tests. Add `flush=all` to the test command to do this (see above example.)
+</div>
+
 <div class="alert" markdown="1">
 If phpunit is not installed globally on your machine, you may need to replace the above usage of `phpunit` with the full
 path (e.g `vendor/bin/phpunit framework/tests`)