ensure kfp is installed from source

sdk/python/kfp/local/testing_utilities.py

@@ -25,6 +25,7 @@
 from absl.testing import parameterized
 from google.protobuf import json_format
 from google.protobuf import message
+import kfp
 from kfp import components
 from kfp import dsl
 from kfp.local import config as local_config
@@ -82,6 +83,11 @@ def tearDown(self):
         # EXIT: mount KFP dir to enable install from source for docker runner
         docker_task_handler.DockerTaskHandler.get_volumes_to_mount = self.original_get_volumes_to_mount
 
+        kfp_path = os.path.abspath(kfp.__file__)
+        assert os.path.exists(
+            kfp_path
+        ) and 'site-packages' not in kfp_path, "KFP should be installed from source in editable mode to run unit tests. Try 'pip install -e sdk/python'. If you've already done this, it's possible the tests have erroneously changed which KFP source code is under test."
+
     @classmethod
     def setUpClass(cls):
         # ENTER: use local KFP package path for subprocess runner