add basic loop() test

tests/test_loop.py

@@ -0,0 +1,68 @@
+# SPDX-FileCopyrightText: 2023 Vladimír Kotal
+#
+# SPDX-License-Identifier: Unlicense
+
+"""loop() tests"""
+
+import random
+import socket
+import ssl
+import time
+from unittest import TestCase, main
+from unittest.mock import patch
+
+import adafruit_minimqtt.adafruit_minimqtt as MQTT
+
+
+class Loop(TestCase):
+    """basic loop() test"""
+
+    connect_times = []
+    INITIAL_RCS_VAL = 42
+    rcs_val = INITIAL_RCS_VAL
+
+    def fake_wait_for_msg(self):
+        """_wait_for_msg() replacement. Sleeps for 1 second and returns an integer."""
+        time.sleep(1)
+        retval = self.rcs_val
+        self.rcs_val += 1
+        return retval
+
+    def test_loop_basic(self) -> None:
+        """
+        test that loop() returns only after the specified timeout, regardless whether
+        _wait_for_msg() returned repeatedly within that timeout.
+        """
+
+        host = "172.40.0.3"
+        port = 1883
+
+        mqtt_client = MQTT.MQTT(
+            broker=host,
+            port=port,
+            socket_pool=socket,
+            ssl_context=ssl.create_default_context(),
+        )
+
+        with patch.object(mqtt_client, "_wait_for_msg") as mock_method:
+            mock_method.side_effect = self.fake_wait_for_msg
+
+            time_before = time.monotonic()
+            timeout = random.randint(3, 8)
+            rcs = mqtt_client.loop(timeout=timeout)
+            time_after = time.monotonic()
+
+            assert time_after - time_before >= timeout
+            mock_method.assert_called()
+
+            # Check the return value.
+            assert rcs is not None
+            assert len(rcs) > 1
+            expected_rc = self.INITIAL_RCS_VAL
+            for ret_code in rcs:
+                assert ret_code == expected_rc
+                expected_rc += 1
+
+
+if __name__ == "__main__":
+    main()