Rename Query._mapper_zero() to Query._entity_zero()

To be more descriptive of the use of _mapper_zero(), rename
it to _entity_zero(), but also supply a new _mapper_zero() function
that more strictly returns a mapper.  The existing
_entity_zero() function is renamed to _query_entity_zero.
_only_mapper_zero() is removed as it isn't used.  Divide up the
existing calling functions to refer to the appropriate new method.

Change-Id: I8780c3235e87b4936c6daf64d9d299b22b6e1260
Fixes: #3608

2 files changed, 7 insertions, 6 deletions

diff --git a/test/orm/test_froms.py b/test/orm/test_froms.py
index 4246df1f6..b4260674d 100644
--- a/test/orm/test_froms.py
+++ b/test/orm/test_froms.py
@@ -1,6 +1,7 @@
 from sqlalchemy import testing
 from sqlalchemy.testing import (
-    fixtures, eq_, assert_raises, assert_raises_message, AssertsCompiledSQL)
+    fixtures, eq_, is_, assert_raises,
+    assert_raises_message, AssertsCompiledSQL)
 from sqlalchemy import (
     exc as sa_exc, util, Integer, Table, String, ForeignKey, select, func,
     and_, asc, desc, inspect, literal_column, cast, exists, text)
@@ -1737,8 +1738,8 @@ class MixedEntitiesTest(QueryTest, AssertsCompiledSQL):
                 "ON users.id = addresses_1.user_id"),
         ]:
             q = s.query(crit)
-            mzero = q._mapper_zero()
-            assert mzero.mapped_table is q._entity_zero().selectable
+            mzero = q._entity_zero()
+            is_(mzero.mapped_table, q._query_entity_zero().selectable)
             q = q.join(j)
             self.assert_compile(q, exp)
 
@@ -1761,8 +1762,8 @@ class MixedEntitiesTest(QueryTest, AssertsCompiledSQL):
                 "ON users_1.id = addresses_1.user_id")
         ]:
             q = s.query(crit)
-            mzero = q._mapper_zero()
-            assert inspect(mzero).selectable is q._entity_zero().selectable
+            mzero = q._entity_zero()
+            is_(inspect(mzero).selectable, q._query_entity_zero().selectable)
             q = q.join(j)
             self.assert_compile(q, exp)
 
diff --git a/test/orm/test_query.py b/test/orm/test_query.py
index cdc4ac2c2..d79de1d96 100644
--- a/test/orm/test_query.py
+++ b/test/orm/test_query.py
@@ -805,7 +805,7 @@ class InvalidGenerationsTest(QueryTest, AssertsCompiledSQL):
             text("select * from table"))
         assert_raises(sa_exc.InvalidRequestError, q.with_polymorphic, User)
 
-    def test_mapper_zero(self):
+    def test_only_full_mapper_zero(self):
         User, Address = self.classes.User, self.classes.Address
 
         s = create_session()