Suggested restructuring from review.

* Independent test_epoch() method.
* Reduce diff for constant test vector, remove unpacking.
* Avoid use of internal constants (except the OFFSET one tested above)
  in dynamic unpacking test vector.

Author: acolomb

test/test_time.py

@@ -1,3 +1,4 @@
+import struct
 import time
 import unittest
 from datetime import datetime
@@ -9,38 +10,37 @@
 
 class TestTime(unittest.TestCase):
 
+    def test_epoch(self):
+        """Verify that the epoch matches the standard definition."""
+        epoch = datetime.strptime(
+            "1984-01-01 00:00:00 +0000", "%Y-%m-%d %H:%M:%S %z"
+        ).timestamp()
+        self.assertEqual(int(epoch), canopen.timestamp.OFFSET)
+
     def test_time_producer(self):
         network = canopen.Network()
         network.NOTIFIER_SHUTDOWN_TIMEOUT = 0.0
         network.connect(interface="virtual", receive_own_messages=True)
         producer = canopen.timestamp.TimeProducer(network)
 
-        # Test that the epoch is correct
-        epoch = datetime.strptime(
-            "1984-01-01 00:00:00 +0000", "%Y-%m-%d %H:%M:%S %z"
-        ).timestamp()
-        self.assertEqual(int(epoch), canopen.timestamp.OFFSET)
+        # Provide a specific time to verify the proper encoding
+        producer.transmit(1_927_999_438)  # 2031-02-04T19:23:58+00:00
+        msg = network.bus.recv(1)
+        self.assertEqual(msg.arbitration_id, 0x100)
+        self.assertEqual(msg.dlc, 6)
+        self.assertEqual(msg.data, b"\xb0\xa4\x29\x04\x31\x43")
 
+        # Test again with the current time as implicit timestamp
         current = time.time()
         with patch("canopen.timestamp.time.time", return_value=current):
-            current_in_epoch = current - epoch
-
-            # Test it looking up the current time
+            current_from_epoch = current - canopen.timestamp.OFFSET
             producer.transmit()
             msg = network.bus.recv(1)
             self.assertEqual(msg.arbitration_id, 0x100)
             self.assertEqual(msg.dlc, 6)
-            ms, days = canopen.timestamp.TIME_OF_DAY_STRUCT.unpack(msg.data)
-            self.assertEqual(days, int(current_in_epoch) // canopen.timestamp.ONE_DAY)
-            self.assertEqual(ms, int((current_in_epoch % canopen.timestamp.ONE_DAY) * 1000))
-
-            # Provide a specific time to verify the proper encoding
-            faketime = 1_927_999_438  # 2031-02-04 19:23:58
-            producer.transmit(faketime)
-            msg = network.bus.recv(1)
-            self.assertEqual(msg.arbitration_id, 0x100)
-            self.assertEqual(msg.dlc, 6)
-            self.assertEqual(msg.data, b"\xb0\xa4\x29\x04\x31\x43")
+            ms, days = struct.unpack("<LH", msg.data)
+            self.assertEqual(days, int(current_from_epoch) // 86400)
+            self.assertEqual(ms, int(current_from_epoch % 86400 * 1000))
 
         network.disconnect()