Lua: Test assertions don't have an error margin

Exercism Bugs & Feature Requests
1

Discord post: Link

Recently I found a very bizarre yet consistent test failure on the Lua track, car-assemble exercise:

image

It was the only remaining test that wasn’t succesful. Here’s my code:

local cars = {}

-- returns the amount of working cars produced by the assembly line every hour
function cars.calculate_working_cars_per_hour(production_rate, success_rate)
  return production_rate * (success_rate / 100)
end

-- returns the amount of working cars produced by the assembly line every minute
function cars.calculate_working_cars_per_minute(production_rate, success_rate)
  return cars.calculate_working_cars_per_hour(production_rate, success_rate) // 60
end

-- returns the cost of producing the given number of cars
function cars.calculate_cost(cars_count)
  return (95000 * (cars_count // 10)) + (10000 * (cars_count % 10))
end

return cars

It’s clear that there should be some kind of an error bar to eliminate such failures, as suggested by @iHiD on Discord.

Thanks!

2

As will probably be obvious to maintainers, my first thought was that it looks to me like an issue with the tests at a glance. I’d guess they’re comparing two floating point numbers without error bars.

3

You’ll get a different result if you remove the parentheses.

4

It works this way, but that failure is still very weird. It’s pretty natural for one to try and divide the percentage by 100 first before doing any multiplication.