A quick-and-dirty list comparison function in Lua that visualizes each list, handling sparse arrays correctly.

compareList.lua

local function compareList(list, len)
		-- We use varargs here since spare arrays make Lua upset
		return function(...)
			len = len or select("#", ...)

			local hasDifference = false
			local differentIndexes = {}

			for i = 1, len do
				if list[i] ~= select(i, ...) then
					differentIndexes[i] = true
					hasDifference = true
				end
			end

			if hasDifference then
				local expectedList = {}
				local foundList = {}
				local expectedDifference = {}
				local foundDifference = {}

				for i = 1, len do
					local expected = tostring((select(i, ...)))
					local found = tostring(list[i])

					local expectedLen = #expected
					local foundLen = #found

					if expectedLen > foundLen then
						found = found .. (" "):rep(expectedLen - foundLen)
					elseif foundLen > expectedLen then
						expected = expected .. (" "):rep(foundLen - expectedLen)
					end

					table.insert(expectedList, expected)
					table.insert(foundList, found)

					if differentIndexes[i] then
						table.insert(expectedDifference, ("^"):rep(expectedLen) .. (" "):rep(#expected - expectedLen))
						table.insert(foundDifference, ("^"):rep(foundLen) .. (" "):rep(#found - foundLen))
					else
						table.insert(expectedDifference, (" "):rep(#expected))
						table.insert(foundDifference, (" "):rep(#found))
					end
				end

				local message = ("Lists were different!\nExpected:\n%s\n%s\nFound:\n%s\n%s"):format(
					table.concat(expectedList, ", "),
					table.concat(expectedDifference, "  "),
					table.concat(foundList, ", "),
					table.concat(foundDifference, "  ")
				)

				error(message, 2)
			end
		end
	end