mounts: add mounts_module_fixture to allow testing mount modules

Similar to `stages` and `sources` we need some basic infrastructure
so that we can use a `mounts_module` fixture for the coming tests
to the mount modules.

mounts/test/conftest.py

@@ -0,0 +1,33 @@
+import os
+import pathlib
+from types import ModuleType
+
+import pytest
+
+from osbuild import mounts, testutil
+from osbuild.testutil.imports import import_module_from_path
+
+
+@pytest.fixture(name="mounts_module")
+def mounts_module_fixture(request: pytest.FixtureRequest) -> ModuleType:
+    """mounts_module is a fixture that imports a stage module by its name
+    defined in MOUNTS_NAME in the test module.
+    """
+    if not hasattr(request.module, "MOUNTS_NAME"):
+        raise ValueError("mounts_module fixture must be used in a test module that defines MOUNTS_NAME")
+
+    mounts_name = request.module.MOUNTS_NAME
+    caller_dir = pathlib.Path(request.node.fspath).parent
+    module_path = caller_dir.parent / mounts_name
+    return import_module_from_path("mounts", os.fspath(module_path))
+
+
+@pytest.fixture
+def mounts_service(mounts_module) -> ModuleType:
+    """mounts_service is a fixture that imports a mounts module by its name
+    defined in MOUNTS_NAME in the test module and returns a MountsService
+    """
+    service_cls = testutil.find_one_subclass_in_module(mounts_module, mounts.MountService)
+    fd = testutil.make_fake_service_fd()
+    srv_obj = service_cls.from_args(["--service-fd", str(fd)])
+    return srv_obj

tox.ini

@@ -24,7 +24,7 @@ deps =
     requests
 
 setenv =
-    LINTABLES = osbuild/ assemblers/* devices/* inputs/*.* mounts/* runners/* sources/*.* stages/*.* inputs/test/*.py stages/test/*.py sources/test/*.py test/ tools/
+    LINTABLES = osbuild/ assemblers/* devices/* inputs/*.* mounts/*.* mounts/test/*.py runners/* sources/*.* stages/*.* inputs/test/*.py stages/test/*.py sources/test/*.py test/ tools/
     LINTABLES_EXCLUDES = "*.json,*.sh"
     LINTABLES_EXCLUDES_RE = ".*\.json$,.*\.sh"
     TYPEABLES = osbuild