diff --git a/test/test_nmt.py b/test/test_nmt.py
index e4bb607b..5acda27d 100644
--- a/test/test_nmt.py
+++ b/test/test_nmt.py
@@ -1,6 +1,7 @@
 import time
 import unittest
 
+import can
 import canopen
 from canopen.nmt import NMT_STATES, NMT_COMMANDS
 from .util import SAMPLE_EDS
@@ -36,23 +37,101 @@ def test_state_set_invalid(self):
         with self.assertRaisesRegex(ValueError, "INVALID"):
             self.nmt.state = "INVALID"
 
-    def test_state_get_invalid(self):
-        # This is a known bug; it will be changed in gh-500.
-        self.nmt._state = 255
-        self.assertEqual(self.nmt.state, 255)
+
+class TestNmtMaster(unittest.TestCase):
+    NODE_ID = 2
+    COB_ID = 0x700 + NODE_ID
+    PERIOD = 0.01
+    TIMEOUT = PERIOD * 2
+
+    def setUp(self):
+        bus = can.ThreadSafeBus(
+            interface="virtual",
+            channel="test",
+            receive_own_messages=True,
+        )
+        net = canopen.Network(bus)
+        net.connect()
+        with self.assertLogs():
+            node = net.add_node(self.NODE_ID, SAMPLE_EDS)
+
+        self.bus = bus
+        self.net = net
+        self.node = node
+
+    def tearDown(self):
+        self.net.disconnect()
+
+    def test_nmt_master_no_heartbeat(self):
+        with self.assertRaisesRegex(canopen.nmt.NmtError, "heartbeat"):
+            self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
+        with self.assertRaisesRegex(canopen.nmt.NmtError, "boot-up"):
+            self.node.nmt.wait_for_bootup(self.TIMEOUT)
+
+    def test_nmt_master_on_heartbeat(self):
+        # Skip the special INITIALISING case.
+        for code in [st for st in NMT_STATES if st != 0]:
+            with self.subTest(code=code):
+                data = bytes([code])
+                task = self.net.send_periodic(self.COB_ID, data, self.PERIOD)
+                self.addCleanup(task.stop)
+                actual = self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
+                task.stop()
+                expected = NMT_STATES[code]
+                self.assertEqual(actual, expected)
+
+    def test_nmt_master_on_heartbeat_initialising(self):
+        task = self.net.send_periodic(self.COB_ID, b"\x00", self.PERIOD)
+        self.addCleanup(task.stop)
+        self.node.nmt.wait_for_bootup(self.TIMEOUT)
+        state = self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
+        self.assertEqual(state, "PRE-OPERATIONAL")
+
+    def test_nmt_master_on_heartbeat_unknown_state(self):
+        task = self.net.send_periodic(self.COB_ID, b"\xcb", self.PERIOD)
+        self.addCleanup(task.stop)
+        state = self.node.nmt.wait_for_heartbeat(self.TIMEOUT)
+        # Expect the high bit to be masked out, and the resulting integer
+        # returned as it is. See gh-500 for the data type inconsistency.
+        self.assertEqual(state, 0x4b)
+
+    def test_nmt_master_add_heartbeat_callback(self):
+        from threading import Event
+        event = Event()
+        state = None
+        def hook(st):
+            nonlocal state
+            state = st
+            event.set()
+        self.node.nmt.add_heartbeat_callback(hook)
+        self.net.send_message(self.COB_ID, bytes([127]))
+        self.assertTrue(event.wait(self.TIMEOUT))
+        self.assertEqual(state, 127)
+
+    def test_nmt_master_node_guarding(self):
+        self.node.nmt.start_node_guarding(self.PERIOD)
+        msg = self.bus.recv(self.TIMEOUT)
+        self.assertIsNotNone(msg)
+        self.assertEqual(msg.arbitration_id, self.COB_ID)
+        self.assertEqual(msg.dlc, 0)
+
+        self.node.nmt.stop_node_guarding()
+        self.assertIsNone(self.bus.recv(self.TIMEOUT))
 
 
 class TestNmtSlave(unittest.TestCase):
     def setUp(self):
         self.network1 = canopen.Network()
         self.network1.connect("test", interface="virtual")
-        self.remote_node = self.network1.add_node(2, SAMPLE_EDS)
+        with self.assertLogs():
+            self.remote_node = self.network1.add_node(2, SAMPLE_EDS)
 
         self.network2 = canopen.Network()
         self.network2.connect("test", interface="virtual")
-        self.local_node = self.network2.create_node(2, SAMPLE_EDS)
-        self.remote_node2 = self.network1.add_node(3, SAMPLE_EDS)
-        self.local_node2 = self.network2.create_node(3, SAMPLE_EDS)
+        with self.assertLogs():
+            self.local_node = self.network2.create_node(2, SAMPLE_EDS)
+            self.remote_node2 = self.network1.add_node(3, SAMPLE_EDS)
+            self.local_node2 = self.network2.create_node(3, SAMPLE_EDS)
 
     def tearDown(self):
         self.network1.disconnect()