Implement facade for pytest parametrize, fixtures, classlevel

Add factilities to implement pytest.mark.parametrize and
pytest.fixtures patterns, which largely resemble things we are
already doing.

Ensure a facade is used, so that the test suite remains independent
of py.test, but also tailors the functions to the more limited
scope in which we are using them.

Additionally, create a class-based version that works from the
same facade.

Several old polymorphic tests as well as two of the sql test
are refactored to use the new features.

Change-Id: I6ef8af1dafff92534313016944d447f9439856cf
References: #4896

1 files changed, 70 insertions, 2 deletions

diff --git a/lib/sqlalchemy/testing/config.py b/lib/sqlalchemy/testing/config.py
index f94c5b308..87bbc6a0f 100644
--- a/lib/sqlalchemy/testing/config.py
+++ b/lib/sqlalchemy/testing/config.py
@@ -6,7 +6,6 @@
 # the MIT License: http://www.opensource.org/licenses/mit-license.php
 
 import collections
-from unittest import SkipTest as _skip_test_exception
 
 requirements = None
 db = None
@@ -17,6 +16,75 @@ test_schema = None
 test_schema_2 = None
 _current = None
 
+_fixture_functions = None  # installed by plugin_base
+
+
+def combinations(*comb, **kw):
+    r"""Deliver multiple versions of a test based on positional combinations.
+
+    This is a facade over pytest.mark.parametrize.
+
+
+    :param \*comb: argument combinations.  These are tuples that will be passed
+     positionally to the decorated function.
+
+    :param argnames: optional list of argument names.   These are the names
+     of the arguments in the test function that correspond to the entries
+     in each argument tuple.   pytest.mark.parametrize requires this, however
+     the combinations function will derive it automatically if not present
+     by using ``inspect.getfullargspec(fn).args[1:]``.  Note this assumes the
+     first argument is "self" which is discarded.
+
+    :param id\_: optional id template.  This is a string template that
+     describes how the "id" for each parameter set should be defined, if any.
+     The number of characters in the template should match the number of
+     entries in each argument tuple.   Each character describes how the
+     corresponding entry in the argument tuple should be handled, as far as
+     whether or not it is included in the arguments passed to the function, as
+     well as if it is included in the tokens used to create the id of the
+     parameter set.
+
+     If omitted, the argment combinations are passed to parametrize as is.  If
+     passed, each argument combination is turned into a pytest.param() object,
+     mapping the elements of the argument tuple to produce an id based on a
+     character value in the same position within the string template using the
+     following scheme::
+
+        i - the given argument is a string that is part of the id only, don't
+            pass it as an argument
+
+        n - the given argument should be passed and it should be added to the
+            id by calling the .__name__ attribute
+
+        r - the given argument should be passed and it should be added to the
+            id by calling repr()
+
+        s-  the given argument should be passed and it should be added to the
+            id by calling str()
+
+     e.g.::
+
+        @testing.combinations(
+            (operator.eq, "eq"),
+            (operator.ne, "ne"),
+            (operator.gt, "gt"),
+            (operator.lt, "lt"),
+            id_="na"
+        )
+        def test_operator(self, opfunc, name):
+            pass
+
+    The above combination will call ``.__name__`` on the first member of
+    each tuple and use that as the "id" to pytest.param().
+
+
+    """
+    return _fixture_functions.combinations(*comb, **kw)
+
+
+def fixture(*arg, **kw):
+    return _fixture_functions.fixture(*arg, **kw)
+
 
 class Config(object):
     def __init__(self, db, db_opts, options, file_config):
@@ -94,4 +162,4 @@ class Config(object):
 
 
 def skip_test(msg):
-    raise _skip_test_exception(msg)
+    raise _fixture_functions.skip_test_exception(msg)