Add a test for invalid TOML file

testing/test_findpaths.py

@@ -2,6 +2,7 @@ from pathlib import Path
 from textwrap import dedent
 
 import pytest
+from _pytest.config import UsageError
 from _pytest.config.findpaths import get_common_ancestor
 from _pytest.config.findpaths import get_dirs_from_args
 from _pytest.config.findpaths import load_config_dict_from_file
@@ -52,6 +53,13 @@ class TestLoadConfigDictFromFile:
             load_config_dict_from_file(fn)
 
     def test_invalid_toml_file(self, tmp_path: Path) -> None:
+        """Invalid .toml files should raise `UsageError`."""
+        fn = tmp_path / "myconfig.toml"
+        fn.write_text("]invalid toml[", encoding="utf-8")
+        with pytest.raises(UsageError):
+            load_config_dict_from_file(fn)
+
+    def test_custom_toml_file(self, tmp_path: Path) -> None:
         """.toml files without [tool.pytest.ini_options] are not considered for configuration."""
         fn = tmp_path / "myconfig.toml"
         fn.write_text(