Fix misspecified twilio tests

Prior implementation ran `assert ...MagicMock.called_with(...)`

`called_with` is not a real test method on MagicMock, so it returns a
MagicMock instance by default, which is truthy and evaluates to true
by assert. This test wasn't checking for anything and would pass no
matter what actually happened in the code.

These new tests check for the intended methods being called.

test/test_twilio/test_twilio.py

@@ -34,18 +34,21 @@ def test_get_messages(self):
     def test_get_account_usage(self):
 
         # Make sure that it is calling the correct Twilio methods
+        self.twilio.client.usage.records.today.list.assert_not_called()
         self.twilio.get_account_usage(time_period="today")
-        assert self.twilio.client.usage.records.today.list.called_with(time_period="today")
+        self.twilio.client.usage.records.today.list.assert_called()
+
+        self.twilio.client.usage.records.last_month.list.assert_not_called()
         self.twilio.get_account_usage(time_period="last_month")
-        assert self.twilio.client.usage.records.last_month.list.called_with(
-            time_period="last_month"
-        )
+        self.twilio.client.usage.records.last_month.list.assert_called()
+
+        self.twilio.client.usage.records.this_month.list.assert_not_called()
         self.twilio.get_account_usage(time_period="this_month")
-        assert self.twilio.client.usage.records.this_month.list.called_with(
-            time_period="this_month"
-        )
+        self.twilio.client.usage.records.this_month.list.assert_called()
+
+        self.twilio.client.usage.records.yesterday.list.assert_not_called()
         self.twilio.get_account_usage(time_period="yesterday")
-        assert self.twilio.client.usage.records.today.list.called_with(time_period="yesterday")
+        self.twilio.client.usage.records.yesterday.list.assert_called()
 
         # Make sure that it is calling the correct Twilio methods
         self.twilio.get_account_usage(time_period="daily", start_date="10-19-2019")