Introduce flag combinations fixture

A helper for @testing.combinations when we just have lots of
true/false combinations as is the case with some ORM tests.

Change-Id: I9f2de97ce5b2487411ed610b8d41169c1052bd8f

2 files changed, 51 insertions, 0 deletions

diff --git a/lib/sqlalchemy/testing/__init__.py b/lib/sqlalchemy/testing/__init__.py
index 1e506ccb1..a1f4b12ba 100644
--- a/lib/sqlalchemy/testing/__init__.py
+++ b/lib/sqlalchemy/testing/__init__.py
@@ -52,6 +52,7 @@ from .exclusions import skip  # noqa
 from .exclusions import skip_if  # noqa
 from .util import adict  # noqa
 from .util import fail  # noqa
+from .util import flag_combinations  # noqa
 from .util import force_drop_names  # noqa
 from .util import metadata_fixture  # noqa
 from .util import provide_metadata  # noqa
diff --git a/lib/sqlalchemy/testing/util.py b/lib/sqlalchemy/testing/util.py
index 64738ad2f..87c461fd2 100644
--- a/lib/sqlalchemy/testing/util.py
+++ b/lib/sqlalchemy/testing/util.py
@@ -211,6 +211,56 @@ def provide_metadata(fn, *args, **kw):
         self.metadata = prev_meta
 
 
+def flag_combinations(*combinations):
+    """A facade around @testing.combinations() oriented towards boolean
+    keyword-based arguments.
+
+    Basically generates a nice looking identifier based on the keywords
+    and also sets up the argument names.
+
+    E.g.::
+
+        @testing.flag_combinations(
+            dict(lazy=False, passive=False),
+            dict(lazy=True, passive=False),
+            dict(lazy=False, passive=True),
+            dict(lazy=False, passive=True, raiseload=True),
+        )
+
+
+    would result in::
+
+        @testing.combinations(
+            ('', False, False, False),
+            ('lazy', True, False, False),
+            ('lazy_passive', True, True, False),
+            ('lazy_passive', True, True, True),
+            id_='iaaa',
+            argnames='lazy,passive,raiseload'
+        )
+
+    """
+
+    from . import config
+
+    keys = set()
+
+    for d in combinations:
+        keys.update(d)
+
+    keys = sorted(keys)
+
+    return config.combinations(
+        *[
+            ("_".join(k for k in keys if d.get(k, False)),)
+            + tuple(d.get(k, False) for k in keys)
+            for d in combinations
+        ],
+        id_="i" + ("a" * len(keys)),
+        argnames=",".join(keys)
+    )
+
+
 def metadata_fixture(ddl="function"):
     """Provide MetaData for a pytest fixture."""