Deduplicate worker tests

A lot of the setup and teardown boilerplate for Worker tests was
repeated between tests.

This commit eliminates that and ensures that each test is using the same
process to set up and tear down the worker, by adding a `worker` fixture
and allowing it to be parameterized indirectly.

python/tests/server/conftest.py

@@ -11,6 +11,7 @@
 
 from cog.command import ast_openapi_schema
 from cog.server.http import create_app
+from cog.server.worker import Worker
 
 
 @define
@@ -19,6 +20,23 @@ class AppConfig:
     options: Optional[Dict[str, Any]]
 
 
+@define
+class WorkerConfig:
+    fixture_name: str
+    setup: bool = True
+
+
+def pytest_make_parametrize_id(config, val):
+    """
+    Generates more readable IDs for parametrized tests that use AppConfig or
+    WorkerConfig values.
+    """
+    if isinstance(val, AppConfig):
+        return val.predictor_fixture
+    elif isinstance(val, WorkerConfig):
+        return val.fixture_name
+
+
 def _fixture_path(name):
     # HACK: `name` can either be in the form "<name>.py:Predictor" or just "<name>".
     if ":" not in name:
@@ -51,6 +69,21 @@ def uses_predictor_with_client_options(name, **options):
     )
 
 
+def uses_worker(name_or_names, setup=True):
+    """
+    Decorator for tests that require a Worker instance. `name_or_names` can be
+    a single fixture name, or a sequence (list, tuple) of fixture names. If
+    it's a sequence, the test will be run once for each worker.
+
+    If `setup` is True (the default) setup will be run before the test runs.
+    """
+    if isinstance(name_or_names, (tuple, list)):
+        values = (WorkerConfig(fixture_name=n, setup=setup) for n in name_or_names)
+    else:
+        values = (WorkerConfig(fixture_name=name_or_names, setup=setup),)
+    return pytest.mark.parametrize("worker", values, indirect=True)
+
+
 def make_client(
     fixture_name: str,
     upload_url: Optional[str] = None,
@@ -104,3 +137,15 @@ def static_schema(client) -> dict:
     ref = _fixture_path(client.ref)
     module_path = ref.split(":", 1)[0]
     return ast_openapi_schema.extract_file(module_path)
+
+
+@pytest.fixture
+def worker(request):
+    ref = _fixture_path(request.param.fixture_name)
+    w = Worker(predictor_ref=ref, tee_output=False)
+    if request.param.setup:
+        assert not w.setup().result().error
+    try:
+        yield w
+    finally:
+        w.shutdown()