boardgame.io/src/testing/mock-random.ts

library for turn-based games

import type { RandomAPI } from '../plugins/random/random';
import RandomPlugin from '../plugins/plugin-random';

/**
 * Test helper that creates a plugin to override the built-in random API.
 *
 * @param overrides - A map of method names to mock functions.
 *
 * @example
 * const game = {
 *   plugins: [
 *     MockRandom({ D6: () => 1 }),
 *   ],
 * };
 */
export const MockRandom = (
  overrides: Partial<Record<keyof RandomAPI, (...args: any[]) => any>> = {}
): Omit<typeof RandomPlugin, 'flush'> => {
  // Don’t include the original flush method, otherwise when the
  // built-in random plugin flushes, it won’t have access to the
  // state it needs.
  const { flush, ...rest } = RandomPlugin;
  return {
    ...rest,
    api: (context) => ({ ...RandomPlugin.api(context), ...overrides }),
  };
};