Add path handling test

Author: znicholls

src/pandas_openscm/db/path_handling.py

@@ -48,7 +48,10 @@ def rel_db_validator(self, attribute: attr.Attribute[Any], value: Path) -> None:
             `value` is not within `self.abs`
         """
         if not str(self.abs).endswith(str(value)):
-            msg = f"{value} for {attribute.name} is not within {self.abs=}"
+            msg = (
+                f"{attribute.name} value, {value!r}, "
+                f"is not a sub-path of {self.abs=!r}"
+            )
             raise AssertionError(msg)
 
     @classmethod

tests/unit/database/test_path_handling.py

@@ -0,0 +1,39 @@
+"""
+Tests of `pandas_openscm.db.path_handling`
+"""
+
+import re
+from contextlib import nullcontext as does_not_raise
+from pathlib import Path
+
+import pytest
+
+from pandas_openscm.db.path_handling import DBPath
+
+
+@pytest.mark.parametrize(
+    "abs, rel_db, exp",
+    (
+        (Path("/a/b/c/d.csv"), Path("d.csv"), does_not_raise()),
+        (Path("/a/b/c/d.csv"), Path("c/d.csv"), does_not_raise()),
+        (
+            Path("/a/b/c/d.csv"),
+            Path("e/d.csv"),
+            pytest.raises(
+                AssertionError,
+                match="".join(
+                    (
+                        re.escape("rel_db value, "),
+                        ".*Path",
+                        re.escape(r"('e/d.csv'), is not a sub-path of self.abs="),
+                        ".*Path",
+                        re.escape("('/a/b/c/d.csv')"),
+                    )
+                ),
+            ),
+        ),
+    ),
+)
+def test_rel_db_validator(abs, rel_db, exp):
+    with exp:
+        DBPath(abs=abs, rel_db=rel_db)