Fix flaky tests with in-memory SQLite databases (#569)

* Run garbage collection before asserting SQLite database is cleared in test

* Use unique in-memory database name for each SQLite test

* Run garbage collection after every test

tests/test_databases.py

@@ -115,6 +115,9 @@ def create_test_database():
         engine = sqlalchemy.create_engine(url)
         metadata.drop_all(engine)
 
+    # Run garbage collection to ensure any in-memory databases are dropped
+    gc.collect()
+
 
 def async_adapter(wrapped_func):
     """
@@ -1549,7 +1552,10 @@ async def test_mapping_property_interface(database_url):
 
 @async_adapter
 async def test_should_not_maintain_ref_when_no_cache_param():
-    async with Database("sqlite:///file::memory:", uri=True) as database:
+    async with Database(
+        "sqlite:///file::memory:",
+        uri=True,
+    ) as database:
         query = sqlalchemy.schema.CreateTable(notes)
         await database.execute(query)
 
@@ -1561,7 +1567,10 @@ async def test_should_not_maintain_ref_when_no_cache_param():
 
 @async_adapter
 async def test_should_maintain_ref_when_cache_param():
-    async with Database("sqlite:///file::memory:?cache=shared", uri=True) as database:
+    async with Database(
+        "sqlite:///file::memory:?cache=shared",
+        uri=True,
+    ) as database:
         query = sqlalchemy.schema.CreateTable(notes)
         await database.execute(query)
 
@@ -1577,15 +1586,24 @@ async def test_should_maintain_ref_when_cache_param():
 
 @async_adapter
 async def test_should_remove_ref_on_disconnect():
-    async with Database("sqlite:///file::memory:?cache=shared", uri=True) as database:
+    async with Database(
+        "sqlite:///file::memory:?cache=shared",
+        uri=True,
+    ) as database:
         query = sqlalchemy.schema.CreateTable(notes)
         await database.execute(query)
 
         query = notes.insert()
         values = {"text": "example1", "completed": True}
         await database.execute(query, values)
 
-    async with Database("sqlite:///file::memory:?cache=shared", uri=True) as database:
+    # Run garbage collection to reset the database if we dropped the reference
+    gc.collect()
+
+    async with Database(
+        "sqlite:///file::memory:?cache=shared",
+        uri=True,
+    ) as database:
         query = notes.select()
         with pytest.raises(sqlite3.OperationalError):
             await database.fetch_all(query=query)