Refactor layers; add postgres support.

README.rst

@@ -32,8 +32,9 @@ Installation
 nti.testing can be installed using pip, either from the git repository
 or from PyPI::
 
-  pip install nti.testing
+  pip install nti.testing[testgres]
 
+Use the ``testgres`` extra to be able to use `nti.testing.layers.postgres`.
 
 PyHamcrest
 ==========
@@ -179,7 +180,7 @@ Test Fixtures
 
 Support for test fixtures can be found in `nti.testing.base` and
 `nti.testing.layers`. The ``base`` package includes fully-fleshed
-out base classes for direct use, while the ``layers`` package includes
+out base classes for direct use, while the ``layers`` package mostly includes
 mixins that can be used to construct your own test layers.
 
 The ``base`` package makes a distinction between "normal" and "shared"

setup.py

@@ -13,6 +13,7 @@
     'Acquisition',
     'zope.site',
     'zope.testrunner',
+    'testgres',
 ]
 
 def _read(fname):
@@ -75,6 +76,8 @@ def _read(fname):
             'Sphinx',
             'sphinx_rtd_theme',
         ],
+        'testgres': [
+        ],
     },
     python_requires=">=3.8",
 )

src/nti/testing/__init__.py

@@ -52,6 +52,7 @@
 from .matchers import implements
 from .matchers import verifiably_provides
 from .matchers import validly_provides
+from .matchers import provides
 from .matchers import validated_by
 from .matchers import not_validated_by
 from .matchers import aq_inContextOf
@@ -95,6 +96,7 @@ def transactionCleanUp():
     'implements',
     'verifiably_provides',
     'validly_provides',
+    'provides',
     'validated_by',
     'not_validated_by',
     'aq_inContextOf',