Django Rest Framework APITestCase reques tofrmat

When trying to test apis that are decorated with @api_view I receive a format that does not match to the response when testing it manually. I expect the following format:

{
    "field": "string value"
}

but when I try to post(from tests) I receive error because the format appears to be this one:

{
    "field": ["string_value"]
}

To reproduce this problem:

class Tests(rest_framework.test.APITestCase):
    def test_api(self): 
         ...
         response = self.client.post(url, data)
         ...