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

lib/spack/llnl/util/lang.py

@@ -362,3 +362,15 @@ class RequiredAttributeError(ValueError):
 
     def __init__(self, message):
         super(RequiredAttributeError, self).__init__(message)
+
+
+def duplicate_stream(original):
+    """Duplicates a stream  at the os level.
+
+    :param stream original: original stream to be duplicated. Must have a
+        `fileno` callable attribute.
+
+    :return: duplicate of the original stream
+    :rtype: file like object
+    """
+    return os.fdopen(os.dup(original.fileno()))

lib/spack/llnl/util/tty/log.py

@@ -30,6 +30,7 @@
 import select
 import sys
 
+import llnl.util.lang as lang
 import llnl.util.tty as tty
 import llnl.util.tty.color as color
 
@@ -147,9 +148,7 @@ def __init__(
     def __enter__(self):
         # Sets a daemon that writes to file what it reads from a pipe
         try:
-            fwd_input_stream = os.fdopen(
-                os.dup(self.input_stream.fileno())
-            )
+            fwd_input_stream = lang.duplicate_stream(self.input_stream)
             self.p = multiprocessing.Process(
                 target=self._spawn_writing_daemon,
                 args=(self.read, fwd_input_stream),