Support python 3.7 and 3.8 in tests and travis CI

Some changes in tests were needed to make them pass:
- `issubclass(w[0].category, DeprecationWarning)` - previous version
breaks on python 3.7 executed with PYTHONASYNCIODEBUG=1
- `disable_gc` fixture - I can only suspect that in p3.7 and p3.8
the connection object was automatically garbage collected before the
`gc.collect()` was invoked.
- curosor `async for` usage was incorrect

Author: MateuszCzubak

.travis.yml

@@ -2,6 +2,8 @@ language: python
 
 python:
     - 3.6
+    - 3.7
+    - 3.8
 
 env:
     matrix:

tests/conftest.py

@@ -22,6 +22,18 @@
     uvloop = None
 
 
+@pytest.fixture
+def disable_gc():
+    gc_enabled = gc.isenabled()
+    if gc_enabled:
+        gc.disable()
+        gc.collect()
+    yield
+    if gc_enabled:
+        gc.collect()
+        gc.enable()
+
+
 @pytest.fixture(scope='session')
 def unused_port():
     def f():

tests/test_async_with.py

@@ -131,7 +131,11 @@ async def test_create_pool_deprecations(mysql_params, loop):
             warnings.simplefilter("always")
             async with pool.get() as conn:
                 pass
-    assert issubclass(w[-1].category, DeprecationWarning)
+    # The first warning emitted is expected to be DeprecationWarning:
+    # in the past, we used to check for the last one but this assumption
+    # breaks under Python 3.7 that also emits a `ResourceWarning` when
+    # executed with `PYTHONASYNCIODEBUG=1`.
+    assert issubclass(w[0].category, DeprecationWarning)
     assert conn.closed
 
     async with create_pool(loop=loop, **mysql_params) as pool:
@@ -149,9 +153,10 @@ async def test_sa_connection(table, mysql_params, loop):
         connection = await engine.acquire()
         assert not connection.closed
         async with connection:
-            ret = []
-            async for i in connection.execute(tbl.select()):
-                ret.append(i)
+            async with connection.execute(tbl.select()) as cursor:
+                ret = []
+                async for i in cursor:
+                    ret.append(i)
             assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
         assert connection.closed
 
@@ -194,21 +199,23 @@ async def test_sa_transaction_rollback(loop, mysql_params, table):
 async def test_create_engine(loop, mysql_params, table):
     async with sa.create_engine(loop=loop, **mysql_params) as engine:
         async with engine.acquire() as conn:
-            ret = []
-            async for i in conn.execute(tbl.select()):
-                ret.append(i)
-            assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
+            async with conn.execute(tbl.select()) as cursor:
+                ret = []
+                async for i in cursor:
+                    ret.append(i)
+                assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
 
 
 @pytest.mark.run_loop
 async def test_engine(loop, mysql_params, table):
     engine = await sa.create_engine(loop=loop, **mysql_params)
     async with engine:
         async with engine.acquire() as conn:
-            ret = []
-            async for i in conn.execute(tbl.select()):
-                ret.append(i)
-            assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
+            async with conn.execute(tbl.select()) as cursor:
+                ret = []
+                async for i in cursor:
+                    ret.append(i)
+                assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
 
 
 @pytest.mark.run_loop
@@ -218,7 +225,7 @@ async def test_transaction_context_manager(loop, mysql_params, table):
             async with conn.begin() as tr:
                 async with conn.execute(tbl.select()) as cursor:
                     ret = []
-                    async for i in conn.execute(tbl.select()):
+                    async for i in cursor:
                         ret.append(i)
                     assert [(1, 'a'), (2, 'b'), (3, 'c')] == ret
                 assert cursor.closed

tests/test_connection.py

@@ -219,6 +219,7 @@ async def test_connection_double_ensure_closed(connection_creator):
 
 
 @pytest.mark.run_loop
+@pytest.mark.usefixtures("disable_gc")
 async def test___del__(connection_creator):
     conn = await connection_creator()
     with pytest.warns(ResourceWarning):