Rest_Framework APIClient tests return 401 Unauthorized with Token Authentication

I'm writing some tests for my rest_framework API, and I'm using token authentication to secure it. I've decided to use DRF's APIClient class to simulate calls from a user's browser.

I can grab tokens just fine from the API by hitting the authentication endpoint, but when I try to use those tokens to authenticate any further requests to other endpoints, I get back a 401 Unauthorized error with the message, "Invalid token".

Curiously, I can copy-paste the exact same token and make a successful, manual GET request to that exact same endpoint via something like HTTPIE...

Here's my tests.py:

import json

from rest_framework import status
from rest_framework.test import APIClient
from rest_framework.test import APITestCase


class TestUser(object):
    """
    A basic user class to simplify requests to the API
    Tokens can be generated by authing as a user to /v1/auth/
    """
    def __init__(self, token):
        self.client = APIClient()
        self.token = token
        self.client.credentials(HTTP_AUTHORIZATION='Token ' + token)

    def get(self, url):
        print("Token: {0}".format(self.token))
        res = self.client.get(url)
        print('GET {0}: {1}'.format(url, res.data))
        return res

    def post(self, url, data):
        res = self.client.post(url, data, format='json')
        print('POST {0}: {1}'.format(url, res.data))
        return res

    def patch(self, url, data):
        res = self.client.patch(url, data, json=data)
        print('PATCH {0}: {1}'.format(url, res.data))
        return res

    def delete(self, url):
        res = self.client.delete(url)
        print('DELETE {0}: {1}'.format(url, res.data))
        return res


# Grab new tokens every time we run our tests
auth_client = APIClient()

SUPERUSER = TestUser(auth_client.post('/v1/auth/', {'username': 'TestUser',
                                      'password': 'password'}).data['token'])
ADMIN = TestUser(auth_client.post('/v1/auth/', {'username': 'TestUser4',
                                  'password': 'password'}).data['token'])
MANAGER = TestUser(auth_client.post('/v1/auth/', {'username': 'TestUser2',
                                    'password': 'password'}).data['token'])
EMPLOYEE = TestUser(auth_client.post('/v1/auth/', {'username': 'TestUser3',
                                     'password': 'password'}).data['token'])


class AdminSiteCompanies(APITestCase):
    def test_list_crud_permissions(self):
        # GET
        url = "/v1/admin_site/companies/"
        self.assertEqual(SUPERUSER.get(url).status_code, status.HTTP_200_OK)
        self.assertEqual(ADMIN.get(url).status_code, status.HTTP_200_OK)
        self.assertEqual(MANAGER.get(url).status_code, status.HTTP_403_FORBIDDEN)
        self.assertEqual(EMPLOYEE.get(url).status_code, status.HTTP_403_FORBIDDEN)

This is console output from the above test showing that a valid token is received from the API, just before it spits back a 401 when I try to use it in a test:

Creating test database for alias 'default'...
Token: d579dbe4980d8ac451a462fc78cf38f789decddf
GET /v1/admin_site/companies/: {'detail': 'Invalid token.'}
Destroying test database for alias 'default'...

Here's console output from me making a successful manual GET request using HTTPIE and the above token:

D:\Projects\API-Server>http http://127.0.0.1:8000/v1/admin_site/companies/ "Authorization: Token d579dbe4980d8ac451a462fc78cf38f789decddf"
HTTP/1.0 200 OK
Allow: GET, POST, HEAD, OPTIONS
Content-Type: application/json
Date: Fri, 01 May 2015 05:43:59 GMT
Server: WSGIServer/0.2 CPython/3.4.3
Vary: Accept
X-Frame-Options: SAMEORIGIN

[
    {
        "address": "1234 Fake Street",
        "id": 1,
        "name": "FedEx",
        "shift_type": "OE"
    },
    {
        "address": "Bolivia",
        "id": 2,
        "name": "UPS",
        "shift_type": "PS"
    }
]

Here's the relevant bits from my settings.py:

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'rest_framework',
    'rest_framework.authtoken',
    'serverapp',
    'rest_framework_swagger',
)

MIDDLEWARE_CLASSES = (
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
    'django.middleware.security.SecurityMiddleware',
    'serverapp.middlewares.EmployeeMiddleware',
)

ROOT_URLCONF = 'shiftserver.urls'

REST_FRAMEWORK = {
    'DEFAULT_AUTHENTICATION_CLASSES': (
        'rest_framework.authentication.TokenAuthentication',
    ),
    'DEFAULT_PERMISSION_CLASSES': (
        'rest_framework.permissions.IsAuthenticated',
    ),
    'DEFAULT_FILTER_BACKENDS': (
        'rest_framework.filters.DjangoFilterBackend',
    )
}

# Database
# https://docs.djangoproject.com/en/1.8/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}

This is the first time I've ever written tests for Django/rest_framework, so I've been diligently following DRF's documentation on testing and authenticating. No matter what I try, though, I still can't get past this "invalid token" issue.

A friend who's way more versed in DRF than me was left stumped when I asked him for help with this, so hopefully you guys can reveal what we're both missing.