TST+CLN: More slice ordering testing, minor cleanup

Author: moloney

nibabel/nicom/tests/test_dicomwrappers.py

@@ -388,7 +388,7 @@ def fake_frames(seq_name, field_name, value_seq, frame_seq=None):
     class Fake:
         pass
 
-    if frame_seq == None:
+    if frame_seq is None:
         frame_seq = [Fake() for _ in range(len(value_seq))]
     for value, fake_frame in zip(value_seq, frame_seq):
         fake_element = Fake()
@@ -868,6 +868,11 @@ def test_data_fake(self):
         sorted_data = data[..., [3, 1, 2, 0]]
         fake_mf['pixel_array'] = np.rollaxis(sorted_data, 2)
         assert_array_equal(MFW(fake_mf).get_data(), data * 2.0 - 1)
+        # Check slice sorting with negative index / IPP correlation
+        fake_mf.update(fake_shape_dependents(dim_idxs, sid_dim=0, flip_ipp_idx_corr=True))
+        sorted_data = data[..., [0, 2, 1, 3]]
+        fake_mf['pixel_array'] = np.rollaxis(sorted_data, 2)
+        assert_array_equal(MFW(fake_mf).get_data(), data * 2.0 - 1)
         # 5D!
         dim_idxs = [
             [1, 4, 2, 1],