diff --git a/.github/workflows/tox.yml b/.github/workflows/tox.yml
index ef3c5cad..04dfd177 100644
--- a/.github/workflows/tox.yml
+++ b/.github/workflows/tox.yml
@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ["3.6", "3.8"]
+        python-version: ["3.6.15", "3.8.17"]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2
diff --git a/orquesta/expressions/functions/workflow.py b/orquesta/expressions/functions/workflow.py
index e1a173bc..18149e2f 100644
--- a/orquesta/expressions/functions/workflow.py
+++ b/orquesta/expressions/functions/workflow.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import collections
+import collections.abc
 
 from orquesta import constants
 from orquesta import exceptions as exc
diff --git a/orquesta/expressions/jinja.py b/orquesta/expressions/jinja.py
index 0cabe91c..83410b52 100644
--- a/orquesta/expressions/jinja.py
+++ b/orquesta/expressions/jinja.py
@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import collections.abc
 import functools
 import inspect
 import itertools
@@ -215,6 +216,11 @@ def evaluate(cls, text, data=None):
         # Recursively evaluate the expression.
         output = cls._evaluate_and_expand(text, data=data)
 
+        # Fix #247 by casting dict_keys objects to list.  Jinja returns
+        # dict_keys objects from dictionary .keys() method.
+        if isinstance(output, collections.abc.KeysView):
+            output = list(output)
+
         if isinstance(output, str):
             exprs = [cls.strip_delimiter(expr) for expr in cls._regex_parser.findall(output)]
 
diff --git a/orquesta/expressions/yql.py b/orquesta/expressions/yql.py
index 82d40f49..e82f6c66 100644
--- a/orquesta/expressions/yql.py
+++ b/orquesta/expressions/yql.py
@@ -141,7 +141,9 @@ def evaluate(cls, text, data=None):
                 stripped = cls.strip_delimiter(expr)
                 result = cls._engine(stripped).evaluate(context=ctx)
 
-                if inspect.isgenerator(result):
+                # Fix #247 by casting set objects to list.  YAQL returns
+                # set objects from dictionary .keys() method.
+                if inspect.isgenerator(result) or isinstance(result, set):
                     result = list(result)
 
                 if isinstance(result, str):
diff --git a/orquesta/specs/base.py b/orquesta/specs/base.py
index ff297c17..0161a43d 100644
--- a/orquesta/specs/base.py
+++ b/orquesta/specs/base.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import collections
+import collections.abc
 import inspect
 import json
 import jsonschema
diff --git a/orquesta/tests/unit/base.py b/orquesta/tests/unit/base.py
index 9557b07e..51bbc55c 100644
--- a/orquesta/tests/unit/base.py
+++ b/orquesta/tests/unit/base.py
@@ -71,7 +71,7 @@ def assert_graph_equal(self, wf_graph, expected_wf_graph):
         self.assertListEqual(wf_graph_attrs, expected_wf_graph_attrs)
 
 
-class WorkflowSpecTest(unittest.TestCase):
+class WorkflowSpecTest(unittest.TestCase, metaclass=abc.ABCMeta):
     spec_module_name = "mock"
 
     def __init__(self, *args, **kwargs):
@@ -141,7 +141,7 @@ def assert_compose_to_wf_ex_graph(self, wf_name, expected_wf_ex_graph):
         self.assert_graph_equal(wf_ex_graph, expected_wf_ex_graph)
 
 
-class WorkflowConductorTest(WorkflowComposerTest, metaclass=abc.ABCMeta):
+class WorkflowConductorTest(WorkflowComposerTest):
     def format_task_item(
         self,
         task_id,