fix: write tests to avoid regressions

Resolves: #267.

Author: oesteban

nitransforms/tests/test_nonlinear.py

@@ -10,14 +10,24 @@
 
 import numpy as np
 import nibabel as nb
-from nitransforms.resampling import apply
 from nitransforms.base import TransformError
 from nitransforms.nonlinear import (
     BSplineFieldTransform,
     DenseFieldTransform,
 )
 
 
+SOME_TEST_POINTS = np.array(
+    [
+        [0.0, 0.0, 0.0],
+        [1.0, 2.0, 3.0],
+        [10.0, -10.0, 5.0],
+        [-5.0, 7.0, -2.0],
+        [12.0, 0.0, -11.0],
+    ]
+)
+
+
 def test_displacements_init():
     identity1 = DenseFieldTransform(
         np.zeros((10, 10, 10, 3)),
@@ -62,41 +72,12 @@ def test_bsplines_references(testdata_path):
             testdata_path / "someones_bspline_coefficients.nii.gz"
         ).to_field()
 
-    with pytest.raises(TransformError):
-        apply(
-            BSplineFieldTransform(
-                testdata_path / "someones_bspline_coefficients.nii.gz"
-            ),
-            testdata_path / "someones_anatomy.nii.gz",
-        )
-
-    apply(
-        BSplineFieldTransform(testdata_path / "someones_bspline_coefficients.nii.gz"),
-        testdata_path / "someones_anatomy.nii.gz",
+    BSplineFieldTransform(
+        testdata_path / "someones_bspline_coefficients.nii.gz",
         reference=testdata_path / "someones_anatomy.nii.gz",
     )
 
 
-@pytest.mark.xfail(
-    reason="Disable while #266 is developed.",
-    strict=False,
-)
-def test_bspline(tmp_path, testdata_path):
-    """
-    Cross-check B-Splines and deformation field.
-
-    This test is disabled and will be split into two separate tests.
-    The current implementation will be moved into test_resampling.py,
-    since that's what it actually tests.
-
-    In GH-266, this test will be re-implemented by testing the equivalence
-    of the B-Spline and deformation field transforms by calling the
-    transform's `map()` method on points.
-
-    """
-    assert True
-
-
 def test_map_bspline_vs_displacement(tmp_path, testdata_path):
     """Cross-check B-Splines and deformation field."""
     os.chdir(str(tmp_path))
@@ -107,6 +88,8 @@ def test_map_bspline_vs_displacement(tmp_path, testdata_path):
 
     bsplxfm = BSplineFieldTransform(bs_name, reference=img_name).to_field()
     dispxfm = DenseFieldTransform(disp_name)
+    # Interpolating field should be reasonably similar
+    np.testing.assert_allclose(dispxfm._field, bsplxfm._field, atol=1e-1, rtol=1e-4)
 
     # Interpolating the field should be reasonably similar
     np.testing.assert_allclose(dispxfm._field, bsplxfm._field, atol=1e-1, rtol=1e-4)

nitransforms/tests/test_resampling.py

@@ -402,3 +402,33 @@ def test_apply_4d(serialize_4d):
     data = np.asanyarray(moved.dataobj)
     idxs = [tuple(np.argwhere(data[..., i])[0]) for i in range(nvols)]
     assert idxs == [(9 - i, 2, 2) for i in range(nvols)]
+
+
+@pytest.mark.xfail(
+    reason="GH-267: disabled while debugging",
+    strict=False,
+)
+def test_apply_bspline(tmp_path, testdata_path):
+    """Cross-check B-Splines and deformation field."""
+    os.chdir(str(tmp_path))
+
+    img_name = testdata_path / "someones_anatomy.nii.gz"
+    disp_name = testdata_path / "someones_displacement_field.nii.gz"
+    bs_name = testdata_path / "someones_bspline_coefficients.nii.gz"
+
+    bsplxfm = nitnl.BSplineFieldTransform(bs_name, reference=img_name)
+    dispxfm = nitnl.DenseFieldTransform(disp_name)
+
+    out_disp = apply(dispxfm, img_name)
+    out_bspl = apply(bsplxfm, img_name)
+
+    out_disp.to_filename("resampled_field.nii.gz")
+    out_bspl.to_filename("resampled_bsplines.nii.gz")
+
+    assert (
+        np.sqrt(
+            (out_disp.get_fdata(dtype="float32") - out_bspl.get_fdata(dtype="float32"))
+            ** 2
+        ).mean()
+        < 0.2
+    )