Report leaking environment variables in tests

tests/conftest.py

@@ -47,9 +47,30 @@ def restore_env_variables():
     """Ensures that environment variables set during the test do not leak out."""
     env_backup = os.environ.copy()
     yield
+    leaked_vars = os.environ.keys() - env_backup.keys()
     # restore environment as it was before running the test
     os.environ.clear()
     os.environ.update(env_backup)
+    # these are currently known leakers - ideally these would not be allowed
+    allowlist = {
+        "CUDA_DEVICE_ORDER",
+        "LOCAL_RANK",
+        "NODE_RANK",
+        "WORLD_SIZE",
+        "MASTER_ADDR",
+        "MASTER_PORT",
+        "PL_GLOBAL_SEED",
+        "PL_SEED_WORKERS",
+        "WANDB_MODE",
+        "HOROVOD_FUSION_THRESHOLD",
+        "RANK",  # set by DeepSpeed
+        "POPLAR_ENGINE_OPTIONS",  # set by IPUPlugin
+        # set by XLA
+        "XRT_MESH_SERVICE_ADDRESS",
+        "XRT_TORCH_DIST_ROOT",
+    }
+    leaked_vars.difference_update(allowlist)
+    assert not leaked_vars, f"test is leaking environment variable(s): {set(leaked_vars)}"
 
 
 @pytest.fixture(scope="function", autouse=True)

tests/loggers/test_tensorboard.py

@@ -120,6 +120,7 @@ def test_tensorboard_no_name(tmpdir, name):
     assert os.listdir(tmpdir / "version_0")
 
 
+@mock.patch.dict(os.environ, {})
 def test_tensorboard_log_sub_dir(tmpdir):
     class TestLogger(TensorBoardLogger):
         # for reproducibility