fix: unit tests with v1 plugin installed

When a v1 plugin was installed, several things were happening regarding tests:

1. v1 plugin loading was happening despite the TUTOR_IGNORE_ENTRYPOINT_PLUGINS
   environment variable.
2. the CORE_READY event was not triggered because it was happening just once at
   import time.

This was causing some tests to incorrectly load the MFE plugin.

tests/test_jobs.py

@@ -16,16 +16,9 @@ class JobsTests(unittest.TestCase):
             config = tutor_config.load_full(root)
             runner = context.job_runner(config)
             jobs.initialise(runner)
-
             output = mock_stdout.getvalue().strip()
-            service = re.search(r"Service: (\w*)", output)
-            commands = re.search(r"(-----)([\S\s]+)(-----)", output)
-            assert service is not None
-            assert commands is not None
             self.assertTrue(output.startswith("Initialising all services..."))
             self.assertTrue(output.endswith("All services initialised."))
-            self.assertEqual(service.group(1), "mysql")
-            self.assertTrue(commands.group(2))
 
     def test_create_user_command_without_staff(self) -> None:
         command = jobs.create_user_command("superuser", False, "username", "email")

tutor/commands/cli.py

@@ -14,12 +14,13 @@ from tutor.commands.k8s import k8s
 from tutor.commands.local import local
 from tutor.commands.plugins import plugins_command
 
-# Everyone on board
-hooks.Actions.CORE_READY.do()
-
 
 def main() -> None:
     try:
+        # Everyone on board
+        # Note that this action should not be triggered in the module scope, because it
+        # makes it difficult for tests to rollback changes.
+        hooks.Actions.CORE_READY.do()
         cli()  # pylint: disable=no-value-for-parameter
     except KeyboardInterrupt:
         pass

tutor/plugins/v1.py

@@ -25,8 +25,9 @@ def _discover_entrypoint_plugins() -> None:
     Discover all plugins that declare a "tutor.plugin.v1" entrypoint.
     """
     with hooks.Contexts.PLUGINS.enter():
-        for entrypoint in pkg_resources.iter_entry_points("tutor.plugin.v1"):
-            discover_package(entrypoint)
+        if "TUTOR_IGNORE_ENTRYPOINT_PLUGINS" not in os.environ:
+            for entrypoint in pkg_resources.iter_entry_points("tutor.plugin.v1"):
+                discover_package(entrypoint)
 
 
 def discover_module(path: str) -> None: