FIX: Fix miscellaneous oversights in the base DWI model

[jhlegarreta]

Fix miscellaneous oversights in the base DWI model:

• Provide the None default value for the n_jobs kwarg if not provided in the dictionary.

  Fixes:

          n_models = self._fit(
              index,
  >           n_jobs=kwargs.pop("n_jobs"),
              **kwargs,
          )
  E       KeyError: 'n_jobs'
  

• Make the diffusion gradients have a unit norm in the gtab generation fixture.

  Fixes:

          bvecs = np.where(np.isnan(bvecs), 0, bvecs)
          bvecs_close_to_1 = abs(vector_norm(bvecs) - 1) <= atol
          if bvecs.shape[1] != 3:
              raise ValueError("bvecs should be (N, 3)")
          if not np.all(bvecs_close_to_1[dwi_mask]):
  >           raise ValueError(
                  "The vectors in bvecs should be unit (The tolerance "
                  "can be modified as an input parameter)"
              )
  E           ValueError: The vectors in bvecs should be unit (The tolerance can be modified as an input parameter)
  

Add a test to check that DIPY models (e.g. DTI) can be instantiated and that the returned prediction has the expected shape.

[jhlegarreta]

I assume we trust the prediction makes sense and that checking the shape here is enough.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.03%. Comparing base (bb3d129) to head (0a45a48).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
+ Coverage   73.96%   76.03%   +2.06%     
==========================================
  Files          24       24              
  Lines        1402     1402              
  Branches      166      166              
==========================================
+ Hits         1037     1066      +29     
+ Misses        299      263      -36     
- Partials       66       73       +7     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.