fixup test_environment: improve error reporting

Author: mr-c

tests/test_environment.py

@@ -62,7 +62,9 @@ def assert_env_matches(
         if not env_accepts_null():
             e.pop("LC_CTYPE", None)
             e.pop("__CF_USER_TEXT_ENCODING", None)
-        assert len(e) == 0, f"Unexpected environment variable(s): {', '.join(e.keys())}"
+        assert (
+            len(e) == 0
+        ), f"Unexpected environment variable(s): {', '.join(e.keys())} from env {env}."
 
 
 class CheckHolder(ABC):
@@ -311,6 +313,7 @@ def test_preserve_all(
             assert_envvar_matches(checks[vname], vname, env)
         except KeyError as kerr:
             if vname not in os.environ:
+                print(env)
                 raise kerr
             assert val == os.environ[vname]
         except AssertionError: