test-package.diff

$ hg diff
diff --git taskcluster/ci/test/awsy.yml taskcluster/ci/test/awsy.yml
--- taskcluster/ci/test/awsy.yml
+++ taskcluster/ci/test/awsy.yml
@@ -33,16 +33,19 @@ job-defaults:
             .*-devedition/.*: []  # don't run on devedition
             (linux|win|mac)(?!.*shippable).*/opt: []
             default: ['integration', 'mozilla-central', 'mozilla-beta', 'mozilla-release']
     fission-run-on-projects:
         by-test-platform:
             linux1804-64-shippable-qr/opt: ['mozilla-central']
             windows10-64-shippable-qr/opt: ['mozilla-central']
             default: []
+    use-test-packages:
+        - awsy
+        - common
 
 
 awsy:
     description: "Are we slim yet"
     treeherder-symbol: SY(sy)
 
 awsy-tp6:
     description: "Are we slim yet - tp6 pageset"
diff --git taskcluster/taskgraph/transforms/tests.py taskcluster/taskgraph/transforms/tests.py
--- taskcluster/taskgraph/transforms/tests.py
+++ taskcluster/taskgraph/transforms/tests.py
@@ -1452,16 +1452,28 @@ def set_test_manifests(config, tasks):
         # better results.
         if config.params['test_manifest_loader'] != 'default':
             task['chunks'] = "dynamic"
 
         yield task
 
 
 @transforms.add
+def dependent_test_packages(config, tasks):
+    for task in tasks:
+        if task['use-test-packages']:
+            task.setdefault('dependencies', {})
+            for package in (set(task['use-test-packages']) & set(SUPPORTED_PACKAGES.keys())):
+                task['dependencies'][package] = SUPPORTED_PACKAGES[package]
+                task['fetches'][package] = {
+                    # ...
+                }
+
+
+@transforms.add
 def resolve_dynamic_chunks(config, tasks):
     """Determine how many chunks are needed to handle the given set of manifests."""
 
     for task in tasks:
         if task['chunks'] != "dynamic":
             yield task
             continue