autotest: add test for TECS overspeed

Tools/autotest/arduplane.py

@@ -6316,6 +6316,34 @@ class AutoTestPlane(vehicle_test_suite.TestSuite):
         self.context_pop()
         self.reboot_sitl()
 
+    def TECSDescendPitch(self):
+        '''check TECS doesn't over-speed when descending'''
+        self.set_parameters({
+            "TECS_SINK_MAX": 300,
+        })
+
+        airspeed_max = 10
+        self.set_parameter('AIRSPEED_MAX', airspeed_max)
+
+        self.takeoff(400, mode='TAKEOFF', timeout=240)
+
+        loc = self.mav.location()
+        new_alt = 10
+        self.run_cmd_int(
+            mavutil.mavlink.MAV_CMD_DO_REPOSITION,
+            p2=mavutil.mavlink.MAV_DO_REPOSITION_FLAGS_CHANGE_MODE,
+            p5=int(loc.lat * 1e7),
+            p6=int(loc.lng * 1e7),
+            p7=new_alt,    # alt
+            frame=mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT,
+        )
+
+        self.wait_message_field_values('VFR_HUD', {
+            "airspeed": airspeed_max,
+        }, minimum_duration=30, timeout=90, epsilon=1)
+
+        self.disarm_vehicle(force=True)
+
     def GPSPreArms(self):
         '''ensure GPS prearm checks work'''
         self.wait_ready_to_arm()
@@ -6573,6 +6601,7 @@ class AutoTestPlane(vehicle_test_suite.TestSuite):
             self.FRSkyPassThroughSensorIDs,
             self.FRSkyMAVlite,
             self.FRSkyD,
+            self.TECSDescendPitch,
             self.LTM,
             self.DEVO,
             self.AdvancedFailsafe,