enh(tests): add not-oblique test, move tests to test_affines.py

Addressing one of @matthew-brett's comments.

Author: oesteban

nibabel/affines.py

@@ -306,14 +306,6 @@ def obliquity(affine):
     This implementation is inspired by `AFNI's implementation
     <https://github.com/afni/afni/blob/b6a9f7a21c1f3231ff09efbd861f8975ad48e525/src/thd_coords.c#L660-L698>`_
 
-    >>> affine = np.array([
-    ...    [2.74999725e+00, -2.74999817e-03, 2.74999954e-03, -7.69847980e+01],
-    ...    [2.98603540e-03, 2.73886840e+00, -2.47165887e-01, -8.36692043e+01],
-    ...    [-2.49170222e-03, 2.47168626e-01, 2.73886865e+00, -8.34056848e+01],
-    ...    [ 0.00000000e+00, 0.00000000e+00, 0.00000000e+00, 1.00000000e+00]])
-    >>> abs(5.15699 - obliquity(affine)) < 0.0001
-    True
-
     """
     vs = voxel_sizes(affine)
     fig_merit = (affine[:-1, :-1] / vs[np.newaxis, ...]).max(axis=1).min()

nibabel/tests/test_affines.py

@@ -7,7 +7,7 @@
 
 from ..eulerangles import euler2mat
 from ..affines import (AffineError, apply_affine, append_diag, to_matvec,
-                       from_matvec, dot_reduce, voxel_sizes)
+                       from_matvec, dot_reduce, voxel_sizes, obliquity)
 
 
 from nose.tools import assert_equal, assert_raises
@@ -178,3 +178,13 @@ def test_voxel_sizes():
             rot_affine[:3, :3] = rotation
             full_aff = rot_affine.dot(aff)
             assert_almost_equal(voxel_sizes(full_aff), vox_sizes)
+
+
+def test_obliquity():
+    """Check the calculation of inclination of an affine axes."""
+    aligned = np.diag([2.0, 2.0, 2.3, 1.0])
+    aligned[:-1, -1] = [-10, -10, -7]
+    R = from_matvec(euler2mat(x=0.09, y=0.001, z=0.001), [0.0, 0.0, 0.0])
+    oblique = R.dot(aligned)
+    assert_almost_equal(obliquity(aligned), 0.0)
+    assert_almost_equal(obliquity(oblique), 5.1569948883)