Move MockRequest to helpers

tests/fields/file_fields/helpers.py

@@ -1,3 +1,8 @@
+class MockRequest:
+    def build_absolute_uri(self, value):
+        return 'http://example.com' + value
+
+
 class MockFile:
     def __init__(self, name='', size=0, url=''):
         self.name = name

tests/fields/file_fields/test_file_field.py

@@ -1,12 +1,7 @@
 from rest_framework import serializers
 
 from ..base import FieldValues
-from .helpers import MockFile
-
-
-class MockRequest:
-    def build_absolute_uri(self, value):
-        return 'http://example.com' + value
+from .helpers import MockFile, MockRequest
 
 
 class TestFileField(FieldValues):