Don't serialize POST payload to JSON, Django's TestClient will do that for us.

hc/api/tests/test_create_check.py

@@ -8,8 +8,7 @@ class CreateCheckTestCase(BaseTestCase):
     URL = "/api/v1/checks/"
 
     def post(self, data, expected_error=None, expected_fragment=None):
-        r = self.client.post(self.URL, json.dumps(data),
-                             content_type="application/json")
+        r = self.client.post(self.URL, data, content_type="application/json")
 
         if expected_error:
             self.assertEqual(r.status_code, 400)

hc/api/tests/test_update_check.py

@@ -13,10 +13,7 @@ class UpdateCheckTestCase(BaseTestCase):
 
     def post(self, code, data):
         url = "/api/v1/checks/%s" % code
-        r = self.client.post(url, json.dumps(data),
-                             content_type="application/json")
-
-        return r
+        return self.client.post(url, data, content_type="application/json")
 
     def test_it_works(self):
         r = self.post(self.check.code, {

hc/front/tests/test_add_telegram.py

@@ -46,7 +46,7 @@ class AddTelegramTestCase(BaseTestCase):
                 "text": "/start"
             }
         }
-        r = self.client.post("/integrations/telegram/bot/", json.dumps(data),
+        r = self.client.post("/integrations/telegram/bot/", data,
                              content_type="application/json")
 
         self.assertEqual(r.status_code, 200)
@@ -57,17 +57,17 @@ class AddTelegramTestCase(BaseTestCase):
         samples = ["", "{}"]
 
         # text is missing
-        samples.append(json.dumps({
+        samples.append({
             "message": {"chat": {"id": 123, "type": "group"}}
-        }))
+        })
 
         # bad chat type
-        samples.append(json.dumps({
+        samples.append({
             "message": {
                 "chat": {"id": 123, "type": "invalid"},
                 "text": "/start"
             }
-        }))
+        })
 
         for sample in samples:
             r = self.client.post("/integrations/telegram/bot/", sample,