botframework-webchat-component/src/hooks/internal/useMemoize.spec.js

React component of botframework-webchat

import useMemoize from './useMemoize';

jest.mock('react', () => {
  let lastDeps = [];
  let lastResult;

  function arrayEquals(x, y) {
    return x.length === y.length && x.every((item, index) => Object.is(item, y[index]));
  }

  return {
    ...jest.requireActual('react'),
    useMemo: (fn, deps) => {
      if (!arrayEquals(deps, lastDeps)) {
        lastDeps = deps;
        lastResult = fn();
      }

      return lastResult;
    }
  };
});

test('useMemoize should cache result across runs', () => {
  const expensiveSum = jest.fn((x, y) => x + y);

  // Start a run, all calls to sum() will be cached.
  useMemoize(
    expensiveSum,
    sum => {
      expect(sum(1, 2)).toBe(3); // Not cached, return 3.
      expect(sum(1, 2)).toBe(3); // Cached, return 3.
      expect(sum(2, 4)).toBe(6); // Not cached, return 6.
      expect(sum(1, 2)).toBe(3); // Cached, return 3. This is cached because it is inside the same run.
    },
    []
  );

  expect(expensiveSum).toHaveBeenCalledTimes(2);

  expect(expensiveSum.mock.calls[0]).toEqual([1, 2]);
  expect(expensiveSum.mock.calls[1]).toEqual([2, 4]);

  // After the run, 1 + 2 = 3, and 2 + 4 = 6 is cached.

  // Start another run with previous cache
  useMemoize(
    expensiveSum,
    sum => {
      expect(sum(1, 2)).toBe(3); // Cached from previous run, return 3.
      expect(sum(3, 6)).toBe(9); // Not cached, return 9.
    },
    []
  );

  expect(expensiveSum).toHaveBeenCalledTimes(3);
  expect(expensiveSum.mock.calls[2]).toEqual([3, 6]);

  // After the run, only 1 + 2 = 3 and 3 + 6 = 9 is cached. 2 + 4 is dropped.

  // Start another run with previous cache
  useMemoize(
    expensiveSum,
    sum => {
      expect(sum(2, 4)).toBe(6); // Not cached, return 6
    },
    []
  );

  expect(expensiveSum).toHaveBeenCalledTimes(4);
  expect(expensiveSum.mock.calls[3]).toEqual([2, 4]);
});