Add test cases

[XiaoWinter]

I found a throttling method in the comments section that passed all the current tests but was wrong.So I added a test case to find this type of error.With this wrapping method, if the interval between two calls is greater than 1000ms, the wrapped method becomes invalid.

function throttle(func, period) {
  let savedArgs
  let savedThis
  let start = true

  function runFunc() {
    if (savedArgs) {
      func.apply(savedThis, savedArgs)
      savedArgs = undefined
      setTimeout(runFunc, period)
    }
  }

  function wrapper(...rest) {
    savedThis = this
    savedArgs = rest
    if (start) {
      start = false
      runFunc()
    }
  }
  return wrapper
}