add test

tests/test_model_serializer.py

@@ -63,6 +63,7 @@ class RegularFieldsModel(models.Model):
     slug_field = models.SlugField(max_length=100)
     small_integer_field = models.SmallIntegerField()
     text_field = models.TextField(max_length=100)
+    file_field = models.FileField(max_length=100)
     time_field = models.TimeField()
     url_field = models.URLField(max_length=100)
     custom_field = CustomField()
@@ -181,6 +182,7 @@ class TestRegularFieldMappings(TestCase):
                 slug_field = SlugField(max_length=100)
                 small_integer_field = IntegerField()
                 text_field = CharField(max_length=100, style={'base_template': 'textarea.html'})
+                file_field = FileField(max_length=100)
                 time_field = TimeField()
                 url_field = URLField(max_length=100)
                 custom_field = ModelField(model_field=<tests.test_model_serializer.CustomField: custom_field>)