tst: improve test with more specific inputs

The shape of the output is defined by the reference shape in space, and by the input and the transform in the 4th dimension.

Author: oesteban

nitransforms/tests/test_resampling.py

@@ -56,9 +56,13 @@ def test_apply_singleton_time_dimension():
 
     data = np.reshape(np.arange(27, dtype=np.uint8), (3, 3, 3, 1))
     nii = nb.Nifti1Image(data, np.eye(4))
-    xfm = nitl.Affine(np.eye(4), reference=nii)
+    ref = nb.Nifti1Image(np.zeros((4, 4, 4)), np.eye(4))
+    xfm = nitl.Affine(np.eye(4), reference=ref)
     movednii = apply(xfm, nii)
-    assert movednii.shape == nii.shape
+    assert movednii.shape == ref.shape + (1, )
+
+    movednii = apply(xfm, nii, reference=ref)
+    assert movednii.shape == ref.shape + (1, )
 
 
 @pytest.mark.parametrize(