test: print schema with InputObjectType with DateTime field with default_value (#1293) (#1513)

* test [1293]: regression test print schema with InputObjectType with DateTime field with default_value

* chore: clarify test title and assertion

---------

Co-authored-by: Erik Wrede <erikwrede@users.noreply.github.com>

graphene/tests/issues/test_1293.py

@@ -0,0 +1,41 @@
+# https://github.com/graphql-python/graphene/issues/1293
+
+import datetime
+
+import graphene
+from graphql.utilities import print_schema
+
+
+class Filters(graphene.InputObjectType):
+    datetime_after = graphene.DateTime(
+        required=False,
+        default_value=datetime.datetime.utcfromtimestamp(1434549820776 / 1000),
+    )
+    datetime_before = graphene.DateTime(
+        required=False,
+        default_value=datetime.datetime.utcfromtimestamp(1444549820776 / 1000),
+    )
+
+
+class SetDatetime(graphene.Mutation):
+    class Arguments:
+        filters = Filters(required=True)
+
+    ok = graphene.Boolean()
+
+    def mutate(root, info, filters):
+        return SetDatetime(ok=True)
+
+
+class Query(graphene.ObjectType):
+    goodbye = graphene.String()
+
+
+class Mutations(graphene.ObjectType):
+    set_datetime = SetDatetime.Field()
+
+
+def test_schema_printable_with_default_datetime_value():
+    schema = graphene.Schema(query=Query, mutation=Mutations)
+    schema_str = print_schema(schema.graphql_schema)
+    assert schema_str, "empty schema printed"