Demonstrates an issue with removeSelf as a validity test

main.lua

local widget = require("widget") -- Not used in this Gist, but seems to be necessary
local composer = require("composer")

composer.gotoScene("test_scene")

test_scene.lua

local composer = require("composer")

local Scene = composer.newScene()

--
function Scene:create (event)

end

Scene:addEventListener("create")

--
function Scene:show (event)
	if event.phase == "did" then
		self.group = display.newGroup()

		self.view:insert(self.group)

		timer.performWithDelay(30, function(event)
			if self.group.removeSelf == nil then
				print("GONE!")
				timer.cancel(event.source)
				return
			end

			for i = 1, self.group.numChildren do
				--
			end
		end, 0)

		timer.performWithDelay(2000, function()
			composer.gotoScene("test_scene2")
		end)
	end
end

Scene:addEventListener("show")

--
function Scene:hide (event)
	if event.phase == "did" then
		self.group:removeSelf()
	end
end

Scene:addEventListener("hide")

return Scene

test_scene2.lua

local composer = require("composer")

local Scene = composer.newScene()

--
function Scene:create (event)

end

Scene:addEventListener("create")

--
function Scene:show (event)
	if event.phase == "did" then
		
	end
end

Scene:addEventListener("show")

--
function Scene:hide (event)
	if event.phase == "did" then
		
	end
end

Scene:addEventListener("hide")

return Scene