test: add _warning tests

tests/test_raillabel_providerkit/_util/test_warning.py

@@ -0,0 +1,40 @@
+# Copyright DB Netz AG and contributors
+# SPDX-License-Identifier: Apache-2.0
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(1, str(Path(__file__).parent.parent.parent.parent))
+
+from raillabel._util._warning import _warning, _WarningsLogger
+
+
+def test_issue_warning():
+    with _WarningsLogger() as logger:
+        _warning("lorem ipsum")
+
+    assert logger.warnings == [
+        "lorem ipsum"
+    ]
+
+def test_handover_exception():
+    with pytest.raises(RuntimeError) as error:
+        with _WarningsLogger() as logger:
+            raise RuntimeError("weewoo something went wrong")
+
+def test_clear_warnings():
+    with _WarningsLogger() as logger1:
+        _warning("lorem ipsum")
+
+    with _WarningsLogger() as logger2:
+        pass
+
+    assert len(logger2.warnings) == 0
+
+
+if __name__ == "__main__":
+    os.system("clear")
+    pytest.main([__file__, "--disable-pytest-warnings", "--cache-clear", "-v"])