Async tests w/ setTimeout, Date.now() fail

[luwes]

Description

Pretty simple tests for a throttle and debounce function are failing in async tests. If these are put in the test.serial they do pass.

Test Source

test('more throttling', async t => {
  let counter = 0;
  const incr = () => counter++;
  const throttledIncr = l.throttle(30, incr);

  throttledIncr();
  throttledIncr();
  t.is(counter, 1);
  await delay(85);

  t.is(counter, 2);
  throttledIncr();
  t.is(counter, 3);
});

/**
 * Throttle a function.
 *
 * @func
 * @since v0.2.0
 * @category Function
 * @param  {Number}   wait
 * @param  {Function} fn
 * @param  {Object}   [options]
 * @param  {Boolean}  [options.leading=true] - Trigger a leading function call.
 * @param  {Boolean}  [options.trailing=true] - Trigger a trailing function call.
 * @return {Function}
 */
export default function throttle(wait, fn, options = {}) {
  let timeout, context, args, result;
  let previous = 0;

  const later = function() {
    previous = options.leading === false ? 0 : Date.now();
    timeout = null;
    result = fn.apply(context, args);
    if (!timeout) context = args = null;
  };

  const throttled = function() {
    const now = Date.now();
    if (!previous && options.leading === false) previous = now;
    const remaining = wait - (now - previous);
    context = this;
    args = arguments;
    if (remaining <= 0 || remaining > wait) {
      if (timeout) {
        clearTimeout(timeout);
        timeout = null;
      }
      previous = now;
      result = fn.apply(context, args);
      if (!timeout) context = args = null;
    } else if (!timeout && options.trailing !== false) {
      timeout = setTimeout(later, remaining);
    }
    return result;
  };

  throttled.cancel = function() {
    clearTimeout(timeout);
    previous = 0;
    timeout = context = args = null;
  };

  return throttled;
}

Error Message & Stack Trace

Config

Copy the relevant section from package.json:

{
  "ava": {
    "files": [
      "test/*.js"
    ],
    "sources": [
      "src/*.js"
    ],
    "require": [
      "esm",
      "@babel/register"
    ]
  }
}

Command-Line Arguments

ava

Relevant Links

• luwes/tili@558565c

Environment

Node.js v9.11.1
ava 1.0.0-beta.6
npm 5.6.0

[sindresorhus]

Async testing is inherently unpredictable. The correct way to test time-related things is to either use test.serial or use some timer mocking library (#1827).