test(validation): test pushover validates priority

- test that params passed for priority are correctly validated

[Finishes #150627411]

hc/front/tests/test_add_pushbover.py

@@ -38,3 +38,13 @@ def test_it_validates_nonce(self):
         assert r.status_code == 403
 
     ### Test that pushover validates priority
+    def test_pushover_validates_priority(self):
+        self.client.login(username="alice@example.org", password="password")
+
+        session = self.client.session
+        session["po_nonce"] = "n"
+        session.save()
+
+        params = "pushover_user_key=a&nonce=n&prio=INVALID"
+        r = self.client.get("/integrations/add_pushover/?%s" % params)
+        assert r.status_code == 400