Add a page on testing build-decision

how-to/taskcluster/uploading_an_image.rst

@@ -56,6 +56,8 @@ can load them. The procedure is similar to the one above.
 .. _checkout cache version: https://searchfox.org/mozilla-central/rev/1ca8ea11406642df4a2c6f81f21d683817af568d/.taskcluster.yml#217
 
 
+.. _build-decision-image:
+
 build-decision image
 --------------------
 

how-to/test/build-decision.rst

@@ -0,0 +1,17 @@
+Test Build Decision
+===================
+
+When updating the build-decision image, it's a good idea to run a quick test
+before pushing it live. First :ref:`build and publish <build-decision-image>` a
+new ``build-decision`` image. Once your image is on Docker hub:
+
+1. Open the `cron-task-ci-ci-configuration/test-build-decision`_ hook in
+   Taskcluster web.
+2. Edit the ``image`` field in the hook definition to point to your recently
+   uploaded image. Save the hook.
+3. Fire the hook manually.
+
+You should see a new event for the triggered hook. If it successfully creates a
+Decision task, the test has passed!
+
+.. _cron-task-ci-ci-configuration/test-build-decision: https://firefox-ci-tc.services.mozilla.com/hooks/project-releng/cron-task-ci-ci-configuration%2Ftest-build-decision

how-to/test/index.rst

@@ -6,5 +6,6 @@ This section outlines various guides on how to test changes prior to deploying.
 .. toctree::
    :maxdepth: 1
 
-   Updates <updates>
    autograph
+   Build Decision <build-decision>
+   Updates <updates>