feat: Added section on how to test upstream taskgraph changes on firefox

how-to/test/gecko.rst

@@ -0,0 +1,48 @@
+Test Taskgraph Changes in Gecko
+================================
+
+Testing Locally
+---------------
+
+To test upstream taskgraph changes in a Gecko repository, first make your changes in your local taskgraph repository. Then install that version into the Firefox virtualenv using:
+
+::
+
+   ./mach python --virtualenv taskgraph -m pip install -e /path/to/taskgraph
+
+This will install your local taskgraph along with any new dependencies it may require. Now when you run ``./mach taskgraph``, it will use your local copy instead of a release from PyPI.
+
+.. warning::
+
+    When ``mach`` re-generates the virtualenvs, it will clobber your local install. If this happens you will need to re-install your local copy afterwards.
+
+Testing on Try
+--------------
+
+To test taskgraph changes on Try, you need to modify the requirements file to point to your branch or pull request. This process is more involved than local testing.
+
+1. Modify ``taskcluster/requirements.in`` to reference your taskgraph branch:
+
+   ::
+
+      taskcluster-taskgraph@git+https://github.com/user/taskgraph@refs/pull/123/head
+
+2. Re-compile the requirements file without hashes:
+
+   ::
+
+      pip-compile --no-emit-index-url taskcluster/requirements.in
+
+3. Disable hash verification by setting an environment variable in ``.taskcluster.yml``:
+
+   ::
+
+      PIP_REQUIRE_HASHES: 0
+
+4. Push your changes to Try.
+
+.. warning::
+
+    This process currently requires removing the `--require-hashes flag from mach <https://searchfox.org/mozilla-central/source/python/mach/mach/site.py#1540>`__.
+
+For more details, see the upstream documentation on `Testing Pre-Release Versions of Taskgraph <https://taskcluster-taskgraph.readthedocs.io/en/stable/howto/bootstrap-taskgraph.html#testing-pre-release-versions-of-taskgraph>`__.

how-to/test/index.rst

@@ -11,3 +11,4 @@ This section outlines various guides on how to test changes prior to deploying.
    Updates <updates>
    Run Update Verify Locally <update-verify>
    Test Landoscript <landoscript>
+   Test Taskgraph Changes in Gecko <gecko>