diff --git a/gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2 b/gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
index c174d37e88..3ad8ef7689 100644
--- a/gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
+++ b/gapic/ads-templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
@@ -545,11 +545,15 @@ def test_{{ method_name }}(request_type, transport: str = 'grpc'):
           {% if not field.oneof or field.proto3_optional %}
             {{ field.name }}={{ field.mock_value }},
             {% endif %}{% endfor %}
-            {# This is a hack to only pick one field  #}
+            {# This is a hack to only pick one field #}
             {% for oneof_fields in method.output.oneof_fields().values() %}
-            {% with field = oneof_fields[0] %}
+            {# Take the first non-message oneof field. In the corner case when all the fields of a oneof are messages, the oneof will not be populated #}
+            {# Use an outer if-statement here because `first` raises an error if called on an empty sequence #}
+            {% if (oneof_fields | rejectattr('message') | list) %}
+            {% with field = (oneof_fields | rejectattr('message') | first) %}
             {{ field.name }}={{ field.mock_value }},
             {% endwith %}
+            {% endif %}
             {% endfor %}
         )
         {% endif %}
@@ -959,11 +963,13 @@ def test_{{ method_name }}_rest(request_type, transport: str = 'rest'):
             {% if not field.oneof or field.proto3_optional %}
               {{ field.name }}={{ field.mock_value }},
               {% endif %}{% endfor %}
-              {# This is a hack to only pick one field  #}
+              {# This is a hack to only pick one field #}
               {% for oneof_fields in method.output.oneof_fields().values() %}
-              {% with field = oneof_fields[0] %}
+              {% if (oneof_fields | rejectattr('message') | list) %}
+              {% with field = (oneof_fields | rejectattr('message') | first) %}
               {{ field.name }}={{ field.mock_value }},
               {% endwith %}
+              {% endif %}
               {% endfor %}
         )
         {% endif %}
@@ -1029,11 +1035,13 @@ def test_{{ method.name|snake_case }}_rest(request_type):
             {% if not field.oneof or field.proto3_optional %}
               {{ field.name }}={{ field.mock_value }},
               {% endif %}{% endfor %}
-              {# This is a hack to only pick one field  #}
+              {# This is a hack to only pick one field #}
               {% for oneof_fields in method.output.oneof_fields().values() %}
-              {% with field = oneof_fields[0] %}
+              {% if (oneof_fields | rejectattr('message') | list) %}
+              {% with field = (oneof_fields | rejectattr('message') | first) %}
               {{ field.name }}={{ field.mock_value }},
               {% endwith %}
+              {% endif %}
               {% endfor %}
         )
         {% endif %}
diff --git a/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2 b/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2
index 952751323b..2d895cab03 100644
--- a/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2
+++ b/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2
@@ -34,11 +34,15 @@ def test_{{ method_name }}(request_type, transport: str = 'grpc'):
           {% if not field.oneof or field.proto3_optional %}
             {{ field.name }}={{ field.mock_value }},
             {% endif %}{% endfor %}
-            {# This is a hack to only pick one field  #}
+            {# This is a hack to only pick one field #}
             {% for oneof_fields in method.output.oneof_fields().values() %}
-            {% with field = oneof_fields[0] %}
+            {# Take the first non-message oneof field. In the corner case when all the fields of a oneof are messages, the oneof will not be populated #}
+            {# Use an outer if-statement here because `first` raises an error if called on an empty sequence #}
+            {% if (oneof_fields | rejectattr('message') | list) %}
+            {% with field = (oneof_fields | rejectattr('message') | first) %}
             {{ field.name }}={{ field.mock_value }},
             {% endwith %}
+            {% endif %}
             {% endfor %}
         )
         {% endif %}
@@ -903,11 +907,13 @@ def test_{{ method_name }}_rest(request_type):
             {% if not field.oneof or field.proto3_optional %}
               {{ field.name }}={{ field.mock_value }},
             {% endif %}{% endfor %}
-              {# This is a hack to only pick one field  #}
-            {% for oneof_fields in method.extended_lro.operation_type.oneof_fields().values() %}
-              {% with field = oneof_fields[0] %}
-              {{ field.name }}={{ field.mock_value }},
-              {% endwith %}
+            {# This is a hack to only pick one field #}
+            {% for oneof_fields in method.output.oneof_fields().values() %}
+            {% if (oneof_fields | rejectattr('message') | list) %}
+            {% with field = (oneof_fields | rejectattr('message') | first) %}
+            {{ field.name }}={{ field.mock_value }},
+            {% endwith %}
+            {% endif %}
             {% endfor %}
         )
         {% else %}
@@ -916,12 +922,14 @@ def test_{{ method_name }}_rest(request_type):
             {% if not field.oneof or field.proto3_optional %}
               {{ field.name }}={{ field.mock_value }},
               {% endif %}{% endfor %}
-              {# This is a hack to only pick one field  #}
-              {% for oneof_fields in method.output.oneof_fields().values() %}
-              {% with field = oneof_fields[0] %}
-              {{ field.name }}={{ field.mock_value }},
-              {% endwith %}
-              {% endfor %}
+            {# This is a hack to only pick one field #}
+            {% for oneof_fields in method.output.oneof_fields().values() %}
+            {% if (oneof_fields | rejectattr('message') | list) %}
+            {% with field = (oneof_fields | rejectattr('message') | first) %}
+            {{ field.name }}={{ field.mock_value }},
+            {% endwith %}
+            {% endif %}
+            {% endfor %}
         )
         {% endif %}
 
diff --git a/tests/fragments/test_oneof_imported_response.proto b/tests/fragments/test_oneof_imported_response.proto
new file mode 100644
index 0000000000..53f2a2cbd2
--- /dev/null
+++ b/tests/fragments/test_oneof_imported_response.proto
@@ -0,0 +1,41 @@
+// Copyright (C) 2021  Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.fragment;
+
+import "google/api/client.proto";
+import "import.proto";
+
+service MyService {
+  option (google.api.default_host) = "my.example.com";
+  rpc MyMethod(MethodRequest) returns (MethodResponse) {}
+}
+
+message MethodRequest {
+  string input = 1;
+}
+
+message Container {
+  Import import = 1;
+}
+
+message MethodResponse {
+  string parent = 1;
+  oneof format {
+    Container container = 2;
+    string name = 3;
+  }
+}
diff --git a/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py b/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
index a11636125c..079e9cd542 100755
--- a/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
+++ b/tests/integration/goldens/logging/tests/unit/gapic/logging_v2/test_config_service_v2.py
@@ -3248,7 +3248,6 @@ def test_get_sink(request_type, transport: str = 'grpc'):
             output_version_format=logging_config.LogSink.VersionFormat.V2,
             writer_identity='writer_identity_value',
             include_children=True,
-            bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
         response = client.get_sink(request)
 
@@ -3509,7 +3508,6 @@ def test_create_sink(request_type, transport: str = 'grpc'):
             output_version_format=logging_config.LogSink.VersionFormat.V2,
             writer_identity='writer_identity_value',
             include_children=True,
-            bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
         response = client.create_sink(request)
 
@@ -3780,7 +3778,6 @@ def test_update_sink(request_type, transport: str = 'grpc'):
             output_version_format=logging_config.LogSink.VersionFormat.V2,
             writer_identity='writer_identity_value',
             include_children=True,
-            bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
         response = client.update_sink(request)
 
@@ -8546,7 +8543,6 @@ def test_get_sink_rest(request_type):
               output_version_format=logging_config.LogSink.VersionFormat.V2,
               writer_identity='writer_identity_value',
               include_children=True,
-              bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
 
         # Wrap the value into a proper Response obj
@@ -8794,7 +8790,6 @@ def test_create_sink_rest(request_type):
               output_version_format=logging_config.LogSink.VersionFormat.V2,
               writer_identity='writer_identity_value',
               include_children=True,
-              bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
 
         # Wrap the value into a proper Response obj
@@ -9048,7 +9043,6 @@ def test_update_sink_rest(request_type):
               output_version_format=logging_config.LogSink.VersionFormat.V2,
               writer_identity='writer_identity_value',
               include_children=True,
-              bigquery_options=logging_config.BigQueryOptions(use_partitioned_tables=True),
         )
 
         # Wrap the value into a proper Response obj