enh: expand test coverage

nitransforms/tests/test_resampling.py

@@ -15,7 +15,7 @@
 from nitransforms import nonlinear as nitnl
 from nitransforms import manip as nitm
 from nitransforms import io
-from nitransforms.resampling import apply
+from nitransforms.resampling import apply, _apply_volume
 
 RMSE_TOL_LINEAR = 0.09
 RMSE_TOL_NONLINEAR = 0.05
@@ -363,3 +363,16 @@ def test_LinearTransformsMapping_apply(
  reference=testdata_path / "sbref.nii.gz",
  serialize_nvols=2 if serialize_4d else np.inf,
  )
+
+
+@pytest.mark.parametrize("t", list(range(4)))
+def test_apply_helper(monkeypatch, t):
+ """Ensure the apply helper function correctly just decorates with index."""
+ from nitransforms.resampling import ndi
+
+ def _retval(*args, **kwargs):
+ return 1
+
+ monkeypatch.setattr(ndi, "map_coordinates", _retval)
+
+ assert _apply_volume(t, None, None) == (t, 1)