fix(tests): correct the location of the Harness cleanup (#1719)

test_get_extensions called cleanup() on the Harness before using it, so
begin() and the assertion ran against an already-cleaned harness. This
only worked because of a Harness bug that leaves a dangling sqlite3
reference; the fix for that bug (canonical/operator#2507) makes cleanup()
tear down properly and breaks the test. Call cleanup() once the harness
is finished with instead.

Signed-off-by: Marcelo Henrique Neppel <marcelo.neppel@canonical.com>

Author: marceloneppel

tests/unit/test_db.py

@@ -175,12 +175,12 @@ def test_get_extensions(harness):
         default: false
         type: boolean"""
     harness = Harness(PostgresqlOperatorCharm, config=config)
-    harness.cleanup()
     harness.begin()
     assert harness.charm.legacy_db_relation._get_extensions(relation) == (
         [extensions[1], extensions[2]],
         {extensions[2]},
     )
+    harness.cleanup()
 
 
 def test_set_up_relation(harness):