autotest: added test for TKOFF_THR_IDLE

Tools/autotest/arduplane.py

@@ -4831,6 +4831,34 @@ def TakeoffGround(self):
 
         self.fly_home_land_and_disarm()
 
+    def TakeoffIdleThrottle(self):
+        '''Apply idle throttle before takeoff.'''
+        self.customise_SITL_commandline(
+            [],
+            model='plane-catapult',
+            defaults_filepath=self.model_defaults_filepath("plane")
+        )
+        self.set_parameters({
+            "TKOFF_THR_IDLE": 20.0,
+            "TKOFF_THR_MINSPD": 3.0,
+        })
+        self.change_mode("TAKEOFF")
+
+        self.wait_ready_to_arm()
+        self.arm_vehicle()
+
+        # Ensure that the throttle rises to idle throttle.
+        expected_idle_throttle = 1000+10*self.get_parameter("TKOFF_THR_IDLE")
+        self.assert_servo_channel_range(3, expected_idle_throttle-10, expected_idle_throttle+10)
+
+        # Launch the catapult
+        self.set_servo(6, 1000)
+
+        self.delay_sim_time(5)
+        self.change_mode('RTL')
+
+        self.fly_home_land_and_disarm()
+
     def DCMFallback(self):
         '''Really annoy the EKF and force fallback'''
         self.reboot_sitl()
@@ -6389,6 +6417,7 @@ def tests1b(self):
             self.TakeoffTakeoff3,
             self.TakeoffTakeoff4,
             self.TakeoffGround,
+            self.TakeoffIdleThrottle,
             self.ForcedDCM,
             self.DCMFallback,
             self.MAVFTP,