AP_Scripting: added example script that causes a hard fault

this exercises rapid fault handling

libraries/AP_Scripting/examples/fault_handling.lua

@@ -0,0 +1,56 @@
+--[[
+   example script to test fault handling with pcall
+--]]
+
+local MAV_SEVERITY = {EMERGENCY=0, ALERT=1, CRITICAL=2, ERROR=3, WARNING=4, NOTICE=5, INFO=6, DEBUG=7}
+
+gcs:send_text(MAV_SEVERITY.INFO, "Loading fault test")
+
+local test_count = 0
+local fault_count = 0
+
+--[[
+   evaluate a lua function and return nil on fault or the functions return value
+--]]
+local function evaluate(f)
+   local ok, s = pcall(f)
+   eval_func = nil
+   if ok then
+      return s
+   end
+   fault_count = fault_count + 1
+   return nil
+end
+
+local function nil_deref()
+   local loc = nil
+   return loc:lat()
+end
+
+local function bad_random()
+   return math.random(1,0)
+end
+
+local function run_test()
+   local script_variant = test_count % 2
+   if script_variant == 0 then
+      evaluate(nil_deref)
+   elseif script_variant == 1 then
+      evaluate(bad_random)
+   end
+end
+
+local function update()
+   if test_count % 100 == 0 then
+      gcs:send_text(MAV_SEVERITY.INFO,string.format("Test %u fault_count %u", test_count, fault_count))
+   end
+   test_count = test_count + 1
+   run_test()
+   assert(fault_count == test_count, "fault and test counts should match")
+   return update,1
+end
+
+gcs:send_text(MAV_SEVERITY.INFO, "Starting fault test in 2 seconds")
+
+-- wait a while for GCS to connect
+return update,2000