RF: Move pytest and pytest-xdist from general requirement into tests_required

[yarikoptic]

not really sure why this didn't give me troubles before but it does now:

reproin@59965c6fd52f:/$ /usr/bin/heudiconv
Traceback (most recent call last):
  File "/usr/bin/heudiconv", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3019, in <module>
    @_call_aside
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3003, in _call_aside
    f(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3032, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 657, in _build_master
    return cls._build_from_requirements(__requires__)
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 670, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
  File "/usr/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 849, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pytest>=3.6' distribution was not found and is required by nipype

• I do not think pytest must be a runtime requirement
• I do not know if there is any negative side-effect (e.g. some unguarded import of nipype at runtime)

[effigies]

How did you install that the dependencies weren't installed?

pytest is in the main dependencies because the following is expected to work out-of-the-box:

import nipype
nipype.test()

[effigies]

Related: #2680.

[effigies]

Eh, nevermind. I think this makes sense. We do perform an import check in nipype.test:

nipype/nipype/__init__.py

Lines 29 to 33 in 799d3f3

	try:
	import pytest
	except:
	raise RuntimeError(
	'py.test not installed, run: pip install pytest')

@satra Any objections?

[codecov-io]

Codecov Report

Merging #2850 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2850      +/-   ##
==========================================
- Coverage   67.47%   67.45%   -0.03%     
==========================================
  Files         341      341              
  Lines       43362    43362              
  Branches     5379     5379              
==========================================
- Hits        29257    29248       -9     
- Misses      13409    13417       +8     
- Partials      696      697       +1

Flag	Coverage Δ
#smoketests	50.53% <ø> (ø)	⬆️
#unittests	64.88% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
nipype/pipeline/plugins/legacymultiproc.py	61.5% <0%> (-4.5%)	⬇️

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[yarikoptic]

For completeness, in my case it was a reproin docker image, which installed python-nipype debian package. pytest I believe is recommended but not strict dependency.

[yarikoptic]

oh, got merged already... just wanted to push more ;) will do in a new PR.