gremlins-ts/src/strategies/distribution.ts

A monkey testing library written in JavaScript, for Node.js and the browser. Use it to check the robustness of web applications by unleashing a horde of undisciplined gremlins.

import { Chance } from "chance";
import { executeInSeries, configurable } from "../utils";
/**
 * Execute all Gremlins randomly following a distribution, separated by a 10ms
 * delay, for 100 times
 *
 * This is the default attack strategy, so selecting no strategy is equivalent to
 *
 *   var distributionStrategy = gremlins.strategies.distribution();
 *   horde.strategy(distributionStrategy);
 *
 * The attack duration is roughly equivalent to delay * nb, although setTimeout
 * may make it longer when delay is small.
 *
 * By default, this strategy uses a uniform distribution, i.e. all gremlins
 * have an equal chance to be selected for the next action.
 *
 * The distribution strategy can be customized as follows:
 *
 *   distributionStrategy.distribution([0.25, 0.25, 0.25, 0.25]); // chances for each gremlin to be selected ; total must equal 1
 *   distributionStrategy.delay(10); // delay in milliseconds between each wave
 *   distributionStrategy.nb(100); // number of waves to execute (can be overridden in params)
 *   distributionStrategy.randomizer(randomizerObject); // inject a randomizer
 *
 * Example usage:
 *
 *   horde.strategy(gremlins.strategies.distribution()
 *     .delay(50)
 *     .distribution([
 *       0.3, // first gremlin
 *       0.3, // second gremlin
 *       0.3, // third gremlin
 *       0.1, // fourth gremlin
 *     ])
 *   )
 */
function getUniformDistribution(gremlins: any[]): number[] {
  const { length } = gremlins;

  if (length === 0) {
    return [];
  }
  const distribution = [];
  const value = 1 / length;
  for (var i = 0; i < length; i++) {
    distribution.push(value);
  }
  return distribution;
}

type Callback = () => void;
type Params = {
  nb: number;
};
type Config = {
  distribution: number[];
  delay: number;
  nb: number;
  randomizer: Chance.Chance;
};

export function distribution() {
  const config: Config = {
    distribution: [], // percentage of each gremlin species ; the sum of all values should equal to 1
    delay: 10, // delay in milliseconds between each wave
    nb: 1000, // number of waves to execute (can be overridden in params)
    randomizer: new Chance()
  };

  let stopped: boolean;
  let doneCallback: Callback | null | undefined = null;

  function distributionStrategy(
    gremlins: Array<() => void>,
    params: Params,
    done: Callback
  ) {
    const nb = params && params.nb ? params.nb : config.nb;
    const gremlinsCopy = [...gremlins];
    const distribution =
      config.distribution.length === 0
        ? getUniformDistribution(gremlinsCopy)
        : config.distribution;
    // @ts-ignore
    const horde = this;

    if (nb === 0) {
      return done();
    }

    stopped = false;
    doneCallback = done; // done can also be called by stop()

    function executeNext(gremlin: () => void, i: number, callback: Function) {
      if (stopped) {
        return;
      }
      if (i >= nb) {
        return callDone();
      }
      executeInSeries([gremlin], [], horde, function() {
        setTimeout(function() {
          executeNext(pickGremlin(gremlinsCopy, distribution), ++i, callback);
        }, config.delay);
      });
    }

    executeNext(pickGremlin(gremlinsCopy, distribution), 0, executeNext);
  }

  function pickGremlin(gremlins: Array<() => void>, distribution: number[]) {
    var chance = 0;
    var random = config.randomizer.floating({ min: 0, max: 1 });
    for (var i = 0, count = gremlins.length; i < count; i++) {
      chance += distribution[i];
      if (random <= chance) {
        return gremlins[i];
      }
    }
    // no gremlin - probably error in the distribution
    return () => undefined;
  }

  distributionStrategy.stop = () => {
    stopped = true;
    setTimeout(callDone, 4);
  };

  function callDone() {
    if (typeof doneCallback === "function") {
      doneCallback();
    }
    doneCallback = null;
  }

  configurable(distributionStrategy, config);

  return distributionStrategy;
}