* Porting: substitute nose with ytest
This huge commit substitutes nose with pytest as a testing system. Things done here:
* deleted external/nose as it is no longer used
* moved mock resources in their own directory 'test/mock/'
* ported two tests (cmd/find, build_system) to pytest native syntax as an example
* build_environment, log: used monkeypatch instead of try/catch
* moved global mocking of fetch_cache to an auto-used fixture
* moved global mocking from test/__init__.py to conftest.py
* made `spack test` a wrapper around pytest
* run-unit-tests: avoid running python 2.6 tests under coverage to speed them up
* use `pytest --cov` instead of coverage run to cut down testing time
* mock/packages_test: moved mock yaml configuration to files instead of leaving it in the code as string literals
* concretize.py: ported tests to native pytest, reverted multiprocessing in pytest.ini as it was creating the wrong report for coveralls
* conftest.py, fixtures: added docstrings
* concretize_preferences.py: uses fixtures instead of subclassing MockPackagesTest
* directory_layout.py: uses fixtures instead of subclassing MockPackagesTest
* install.py: uses fixtures instead of subclassing MockPackagesTest
* optional_deps.py: uses fixtures instead of subclassing MockPackagesTest
optional_deps.py: uses fixtures instead of subclassing MockPackagesTest
* packages.py: uses fixtures instead of subclassing MockPackagesTest
* provider_index.py: uses fixtures instead of subclassing MockPackagesTest
* spec_yaml.py: uses fixtures instead of subclassing MockPackagesTest
* multimethod.py: uses fixtures instead of subclassing MockPackagesTest
* install.py: now uses mock_archive_url
* git_fetch.py: uses fixtures instead of subclassing MockPackagesTest
* hg_fetch.py: uses fixtures instead of subclassing MockPackagesTest
* svn_fetch.py, mirror.py: uses fixtures instead of subclassing MockPackagesTest
repo.py: deleted
* test_compiler_cmd.py: uses fixtures instead of subclassing MockPackagesTest
* cmd/module.py, cmd/uninstall.py: uses fixtures instead of subclassing MockDatabase
* database.py: uses fixtures instead of subclassing MockDatabase, removed mock/database
* pytest: uncluttering fixture implementations
* database: changing the scope to 'module'
* config.py: uses fixtures instead of subclassing MockPackagesTest
* spec_dag.py, spec_semantics.py: uses fixtures instead of subclassing MockPackagesTest
* stage.py: uses fixtures instead of subclassing MockPackagesTest. Removed mock directory
* pytest: added docstrings to all the fixtures
* pytest: final cleanup
* build_system_guess.py: fixed naming and docstrings as suggested by @scheibelp
* spec_syntax.py: added expected failure on parsing multiple specs closes#1976
* Add pytest and pytest-cov to Spack externals.
* Make `spack flake8` ignore externals.
* run-unit-tests runs spack test and not pytest.
* Remove all the special stuff for `spack test`
- Remove `conftest.py` magic and all the special case stuff in `bin/spack`
- Spack commands can optionally take unknown arguments, if they want to
handle them.
- `spack test` is now a command like the others.
- `spack test` now just delegates its arguments to `pytest`, but it does
it by receiving unknown arguments and NOT taking an explicit
help argument.
* Fix error in fixtures.
* Improve `spack test` command a bit.
- Now supports an approximation of the old simple interface
- Also supports full pytest options if you want them.
* Use external coverage instead of pytest-cov
* Make coverage use parallel-mode.
* change __init__.py docs to include pytest
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