diff --git a/tests/conftest.py b/tests/conftest.py
index 2118d241a7..203efeb986 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,19 +1,40 @@
 #
-# Pytest hooks shared across the netlab test tree
+# Shared pytest configuration for the netlab test suite.
+#
+# 1. Prepend the repository root (the directory containing the 'netsim'
+#    package) to sys.path so 'cd tests && pytest' inside a git worktree
+#    imports this checkout's netsim/, not the venv egg-link's (which
+#    usually points at the main checkout).
+#
+# 2. Anchor the working directory to tests/ so the test bodies' relative
+#    globs (e.g. glob.glob('topology/input/*yml')) resolve no matter
+#    where pytest is invoked from.
+#
+# 3. Surface a UserWarning when ruamel.yaml is installed -- the
+#    transformation tests will be slower and create-error-tests.sh is
+#    unsupported (see https://github.com/ipspace/netlab/issues/3345).
 #
 
+import os
+import pathlib
+import sys
+
 import pytest
-from utils import HAS_RUAMEL
+
+_HERE = pathlib.Path(__file__).resolve().parent
+sys.path.insert(0, str(_HERE.parent))
+
+from utils import HAS_RUAMEL  # noqa: E402 -- requires sys.path tweak above
 
 
 def pytest_configure(config: pytest.Config) -> None:
-  if not HAS_RUAMEL:
-    return
-  config.issue_config_time_warning(
-    UserWarning(
-      "ruamel.yaml is installed; transformation tests will be slower and "
-      "`create-error-tests.sh` is unsupported "
-      "(see https://github.com/ipspace/netlab/issues/3345)."
-    ),
-    stacklevel=2,
-  )
+  os.chdir(_HERE)
+  if HAS_RUAMEL:
+    config.issue_config_time_warning(
+      UserWarning(
+        "ruamel.yaml is installed; transformation tests will be slower and "
+        "`create-error-tests.sh` is unsupported "
+        "(see https://github.com/ipspace/netlab/issues/3345)."
+      ),
+      stacklevel=2,
+    )
diff --git a/tests/test_transformation.py b/tests/test_transformation.py
index 08037d75ad..0a37c5d8c0 100755
--- a/tests/test_transformation.py
+++ b/tests/test_transformation.py
@@ -63,12 +63,11 @@ def run_transformation_test(test_case: str, tmpdir: str = '/tmp') -> None:
 
   assert result == expected
   print("... succeeded, string length = %d" % len(result))
-  
+
 @pytest.mark.filterwarnings("ignore::PendingDeprecationWarning")
-def test_xform_cases(tmpdir: str) -> None:
-  print("Starting transformation test cases")
-  for test_case in list(glob.glob('topology/input/*yml')):
-    run_transformation_test(test_case)
+@pytest.mark.parametrize('test_case',sorted(glob.glob('topology/input/*yml')))
+def test_xform_cases(test_case: str, tmpdir: str) -> None:
+  run_transformation_test(test_case)
 
 # Verbose test cases are executed only when we're doing a coverage report
 #
@@ -76,7 +75,8 @@ def test_coverage_verbose_cases(tmpdir: str) -> None:
   if not sys.gettrace():
     return
   log.set_verbose()
-  test_xform_cases(tmpdir)
+  for test_case in sorted(glob.glob('topology/input/*yml')):
+    run_transformation_test(test_case)
 
 def run_error_case(test_case: str) -> None:
   log.set_flag(raise_error = True)
@@ -97,22 +97,16 @@ def run_error_case(test_case: str) -> None:
     assert error_log == log_lines
 
 @pytest.mark.filterwarnings("ignore::PendingDeprecationWarning")
-def test_error_cases() -> None:
-  print("Starting error test cases")
-  for test_case in list(glob.glob('errors/*yml')):
-    run_error_case(test_case)
+@pytest.mark.parametrize('test_case',sorted(glob.glob('errors/*yml')))
+def test_error_cases(test_case: str) -> None:
+  run_error_case(test_case)
 
 @pytest.mark.filterwarnings("ignore::PendingDeprecationWarning")
-def test_coverage_xf_cases() -> None:
-  for test_case in list(glob.glob('coverage/input/*yml')):
-    run_transformation_test(test_case)
+@pytest.mark.parametrize('test_case',sorted(glob.glob('coverage/input/*yml')))
+def test_coverage_xf_cases(test_case: str) -> None:
+  run_transformation_test(test_case)
 
 @pytest.mark.filterwarnings("ignore::PendingDeprecationWarning")
-def test_coverage_errors() -> None:
-  for test_case in list(glob.glob('coverage/errors/*yml')):
-    run_error_case(test_case)
-
-if __name__ == "__main__":
-  test_xform_cases("/tmp")
-#  test_error_cases()
-#  test_minimal_cases()
+@pytest.mark.parametrize('test_case',sorted(glob.glob('coverage/errors/*yml')))
+def test_coverage_errors(test_case: str) -> None:
+  run_error_case(test_case)