Call module directly rather than binary

tests/__init__.py

@@ -1,6 +1,5 @@
 import functools
 import os
-import shutil
 import subprocess
 import time
 from pathlib import Path
@@ -55,7 +54,9 @@ class BaseWorkerTestCase(BaseTestCase):
         self.unused_port = unused_port()
         self.worker_process = subprocess.Popen(
             [
-                shutil.which("ctf"),
+                "python",
+                "-m",
+                "catfish",
                 "start",
                 "--port",
                 str(self.unused_port),