unit tests: replace nose with pytest (#2502)

* 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

bin/spack

@@ -31,6 +31,7 @@ if (sys.version_info[0] > 2) or (sys.version_info[:2] < (2, 6)):
              "This is Python %d.%d.%d." % v_info)
 
 import os
+import inspect
 
 # Find spack's location and its prefix.
 SPACK_FILE = os.path.realpath(os.path.expanduser(__file__))
@@ -129,6 +130,7 @@ parser.add_argument('-V', '--version', action='version',
 # subparser for setup.
 subparsers = parser.add_subparsers(metavar='SUBCOMMAND', dest="command")
 
+
 import spack.cmd
 for cmd in spack.cmd.commands:
     module = spack.cmd.get_module(cmd)
@@ -136,16 +138,8 @@ for cmd in spack.cmd.commands:
     subparser = subparsers.add_parser(cmd_name, help=module.description)
     module.setup_parser(subparser)
 
-# Just print help and exit if run with no arguments at all
-if len(sys.argv) == 1:
-    parser.print_help()
-    sys.exit(1)
 
-# actually parse the args.
-args = parser.parse_args()
-
-
-def main():
+def _main(args, unknown_args):
     # Set up environment based on args.
     tty.set_verbose(args.verbose)
     tty.set_debug(args.debug)
@@ -171,8 +165,21 @@ def main():
 
     # Try to load the particular command asked for and run it
     command = spack.cmd.get_command(args.command.replace('-', '_'))
+
+    # Allow commands to inject an optional argument and get unknown args
+    # if they want to handle them.
+    info = dict(inspect.getmembers(command))
+    varnames = info['__code__'].co_varnames
+    argcount = info['__code__'].co_argcount
+
+    # Actually execute the command
     try:
-        return_val = command(parser, args)
+        if argcount == 3 and varnames[2] == 'unknown_args':
+            return_val = command(parser, args, unknown_args)
+        else:
+            if unknown_args:
+                tty.die('unrecognized arguments: %s' % ' '.join(unknown_args))
+            return_val = command(parser, args)
     except SpackError as e:
         e.die()
     except KeyboardInterrupt:
@@ -188,11 +195,26 @@ def main():
         tty.die("Bad return value from command %s: %s"
                 % (args.command, return_val))
 
-if args.profile:
-    import cProfile
-    cProfile.run('main()', sort='time')
-elif args.pdb:
-    import pdb
-    pdb.run('main()')
-else:
-    main()
+
+def main(args):
+    # Just print help and exit if run with no arguments at all
+    if len(args) == 1:
+        parser.print_help()
+        sys.exit(1)
+
+    # actually parse the args.
+    args, unknown = parser.parse_known_args()
+
+    if args.profile:
+        import cProfile
+        cProfile.runctx('_main(args, unknown)', globals(), locals(),
+                        sort='time')
+    elif args.pdb:
+        import pdb
+        pdb.runctx('_main(args, unknown)', globals(), locals())
+    else:
+        _main(args, unknown)
+
+
+if __name__ == '__main__':
+    main(sys.argv)