inputs: add inputs_service fixture

This new fixture avoids some repetitivness when building tests
for input services.

inputs/test/conftest.py

@@ -1,14 +1,16 @@
+import inspect
 import os
 import pathlib
 from types import ModuleType
 
 import pytest
 
+from osbuild import inputs, testutil
 from osbuild.testutil.imports import import_module_from_path
 
 
-@pytest.fixture
-def inputs_module(request: pytest.FixtureRequest) -> ModuleType:
+@pytest.fixture(name="inputs_module")
+def inputs_module_fixture(request: pytest.FixtureRequest) -> ModuleType:
     """inputs_module is a fixture that imports a stage module by its name
     defined in INPUTS_NAME in the test module.
     """
@@ -19,3 +21,21 @@ def inputs_module(request: pytest.FixtureRequest) -> ModuleType:
     caller_dir = pathlib.Path(request.node.fspath).parent
     module_path = caller_dir.parent / inputs_name
     return import_module_from_path("inputs", os.fspath(module_path))
+
+
+@pytest.fixture
+def inputs_service(inputs_module) -> ModuleType:
+    """inputs_service is a fixture that imports a inputs module by its name
+    defined in INPUTS_NAME in the test module and returns a InputService
+    """
+    service_cls = None
+    for memb in inspect.getmembers(
+            inputs_module,
+            predicate=lambda obj: inspect.isclass(obj) and issubclass(
+                obj, inputs.InputService)):
+        if service_cls:
+            raise ValueError(f"already have {service_cls}, also found {memb}")
+        service_cls = memb[1]
+    fd = testutil.make_fake_service_fd()
+    srv_obj = service_cls.from_args(["--service-fd", str(fd)])
+    return srv_obj