add new variation helper

I'm using a lot of @testing.combinations with either
a boolean True/False, or a series of string names, each indicating
some case to switch on.  I want a descriptive name in the test
run (not True/False) and I don't want to compare strings.

So make a new helper around @combinations that provides an
object interface that has booleans inside of it, prints nicely
in the test output, raises an error if you name the case
incorrectly.

Before:

test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-False-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-False-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-False-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-True-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-True-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[False-True-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-False-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-False-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-False-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-True-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-True-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[True-True-name] PASSED

After:

test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-deferred-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-deferred-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-deferred-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-not_deferred-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-not_deferred-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[not_use_add_property-not_deferred-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-deferred-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-deferred-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-deferred-name] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-not_deferred-both] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-not_deferred-key] PASSED
test/orm/declarative/test_typed_mapping.py::MappedColumnTest::test_separate_name[use_add_property-not_deferred-name] PASSED

Change-Id: Idde87632581ee69e0f47360966758583dfd8baab

2 files changed, 76 insertions, 0 deletions

diff --git a/lib/sqlalchemy/testing/__init__.py b/lib/sqlalchemy/testing/__init__.py
index 76445a444..3a028f002 100644
--- a/lib/sqlalchemy/testing/__init__.py
+++ b/lib/sqlalchemy/testing/__init__.py
@@ -54,6 +54,7 @@ from .config import db
 from .config import fixture
 from .config import requirements as requires
 from .config import skip_test
+from .config import variation
 from .exclusions import _is_excluded
 from .exclusions import _server_version
 from .exclusions import against as _against
diff --git a/lib/sqlalchemy/testing/config.py b/lib/sqlalchemy/testing/config.py
index 44133984b..749d04248 100644
--- a/lib/sqlalchemy/testing/config.py
+++ b/lib/sqlalchemy/testing/config.py
@@ -128,6 +128,81 @@ def combinations_list(
     return combinations(*arg_iterable, **kw)
 
 
+class _variation_base:
+    __slots__ = ("name", "argname")
+
+    def __init__(self, case, argname, case_names):
+        self.name = case
+        self.argname = argname
+        for casename in case_names:
+            setattr(self, casename, casename == case)
+
+    def __bool__(self):
+        return self.name == self.argname
+
+    def __nonzero__(self):
+        return not self.__bool__()
+
+
+def variation(argname, cases):
+    """a helper around testing.combinations that provides a single namespace
+    that can be used as a switch.
+
+    e.g.::
+
+        @testing.variation("querytyp", ["select", "subquery", "legacy_query"])
+        @testing.variation("lazy", ["select", "raise", "raise_on_sql"])
+        def test_thing(
+            self,
+            querytyp,
+            lazy,
+            decl_base
+        ):
+            class Thing(decl_base):
+                __tablename__ = 'thing'
+
+                # use name directly
+                rel = relationship("Rel", lazy=lazy.name)
+
+            # use as a switch
+            if querytyp.select:
+                stmt = select(Thing)
+            elif querytyp.subquery:
+                stmt = select(Thing).subquery()
+            elif querytyp.legacy_query:
+                stmt = Session.query(Thing)
+            else:
+                assert False
+
+
+    The variable provided is a slots object of boolean variables, as well
+    as the name of the case itself under the attribute ".name"
+
+    """
+
+    case_names = [
+        argname if c is True else "not_" + argname if c is False else c
+        for c in cases
+    ]
+
+    typ = type(
+        argname,
+        (_variation_base,),
+        {
+            "__slots__": tuple(case_names),
+        },
+    )
+
+    return combinations(
+        *[
+            (casename, typ(casename, argname, case_names))
+            for casename in case_names
+        ],
+        id_="ia",
+        argnames=argname,
+    )
+
+
 def fixture(*arg: Any, **kw: Any) -> Any:
     return _fixture_functions.fixture(*arg, **kw)