Add a test and impl for map field mock value

gapic/schema/wrappers.py

@@ -110,9 +110,16 @@ def mock_value(self) -> str:
             sub = next(iter(self.type.fields.values()))
             answer = f'{self.type.ident}({sub.name}={sub.mock_value})'
 
-        # If this is a repeated field, then the mock answer should
-        # be a list.
-        if self.repeated:
+        if self.map:
+            # Maps are a special case beacuse they're represented internally as
+            # a list of a generated type with two fields: 'key' and 'value'.
+            answer = '{{{}: {}}}'.format(
+                self.type.fields["key"].mock_value,
+                self.type.fields["value"].mock_value,
+            )
+        elif self.repeated:
+            # If this is a repeated field, then the mock answer should
+            # be a list.
             answer = f'[{answer}]'
 
         # Done; return the mock value.
@@ -568,7 +575,6 @@ def field_headers(self) -> Sequence[str]:
     @utils.cached_property
     def flattened_fields(self) -> Mapping[str, Field]:
         """Return the signature defined for this method."""
-        signatures = self.options.Extensions[client_pb2.method_signature]
         cross_pkg_request = self.input.ident.package != self.ident.package
 
         def filter_fields(sig):
@@ -585,6 +591,7 @@ def filter_fields(sig):
 
                 yield name, field
 
+        signatures = self.options.Extensions[client_pb2.method_signature]
         answer: Dict[str, Field] = collections.OrderedDict(
             name_and_field
             for sig in signatures

gapic/templates/%namespace/%name_%version/%sub/services/%service/client.py.j2

@@ -204,9 +204,11 @@ class {{ service.client_name }}(metaclass={{ service.client_name }}Meta):
         {% endif %} {# different request package #}
 
         {#- Vanilla python protobuf wrapper types cannot _set_ repeated fields #}
-        {%- for key, field in method.flattened_fields.items() if not(field.repeated and method.input.ident.package != method.ident.package) %}
+        {% if method.flattened_fields -%}
         # If we have keyword arguments corresponding to fields on the
         # request, apply these.
+        {% endif -%}
+        {%- for key, field in method.flattened_fields.items() if not(field.repeated and method.input.ident.package != method.ident.package) %}
         if {{ field.name }} is not None:
             request.{{ key }} = {{ field.name }}
         {%- endfor %}

tests/unit/schema/wrappers/test_field.py

@@ -173,6 +173,25 @@ def test_mock_value_repeated():
     assert field.mock_value == "['foo_bar_value']"
 
 
+def test_mock_value_map():
+    entry_msg = make_message(
+        name='SquidEntry',
+        fields=(
+            make_field(name='key', type='TYPE_STRING'),
+            make_field(name='value', type='TYPE_STRING'),
+        ),
+        options=descriptor_pb2.MessageOptions(map_entry=True),
+    )
+    field = make_field(
+        name='squids',
+        type_name='mollusc.SquidEntry',
+        message=entry_msg,
+        label=3,
+        type='TYPE_MESSAGE',
+    )
+    assert field.mock_value == "{'key_value': 'value_value'}"
+
+
 def test_mock_value_enum():
     values = [
         descriptor_pb2.EnumValueDescriptorProto(name='UNSPECIFIED', number=0),
@@ -227,4 +246,26 @@ def make_field(*, message=None, enum=None, **kwargs) -> wrappers.Field:
     if isinstance(kwargs['type'], str):
         kwargs['type'] = T.Value(kwargs['type'])
     field_pb = descriptor_pb2.FieldDescriptorProto(**kwargs)
-    return wrappers.Field(field_pb=field_pb, message=message, enum=enum)
+    field = wrappers.Field(field_pb=field_pb, message=message, enum=enum)
+    return field
+
+
+def make_message(
+    name, package='foo.bar.v1', module='baz', fields=(), meta=None, options=None
+) -> wrappers.MessageType:
+    message_pb = descriptor_pb2.DescriptorProto(
+        name=name,
+        field=[i.field_pb for i in fields],
+        options=options,
+    )
+    return wrappers.MessageType(
+        message_pb=message_pb,
+        fields=collections.OrderedDict((i.name, i) for i in fields),
+        nested_messages={},
+        nested_enums={},
+        meta=meta or metadata.Metadata(address=metadata.Address(
+            name=name,
+            package=tuple(package.split('.')),
+            module=module,
+        )),
+    )