Lycolog

describe('example1', () => {
  it('1', () => {
    expect(1).toBe(1);
  });
  it('2', () => {
    expect(2).toBe(2);
  });
  it('3', () => {
    expect(3).toBe(3);
  });
  it('4', () => {
    expect(4).toBe(4);
  });
  it('5', () => {
    expect(5).toBe(5);
  });
});

describe('example2', () => {
  it('1', () => {
    expect(1).toBe(1);
  });
  it('2', () => {
    expect(2).toBe(2);
  });
  it('3', () => {
    expect(3).toBe(3);
  });
  it('4', () => {
    expect(4).toBe(4);
  });
  it('5', () => {
    expect(5).toBe(5);
  });
});

確認環境一式

以下のリポジトリに確認したソースコードを一式格納しています。

[blogcard https://github.com/Lycolia/jest-memory-leak-example]

メモリリークしていく様子

(41 MB heap size)
(42 MB heap size)
(52 MB heap size)
(51 MB heap size)
(37 MB heap size)
(47 MB heap size)
(47 MB heap size)
(50 MB heap size)
(60 MB heap size)
(60 MB heap size)
(62 MB heap size)
(71 MB heap size)
(73 MB heap size)
(74 MB heap size)
(84 MB heap size)
(85 MB heap size)
(86 MB heap size)
(96 MB heap size)
(97 MB heap size)
(99 MB heap size)
(108 MB heap size)
(110 MB heap size)
(111 MB heap size)
(120 MB heap size)
(122 MB heap size)
(124 MB heap size)
(75 MB heap size)
(83 MB heap size)
(84 MB heap size)
(86 MB heap size)
(96 MB heap size)
(96 MB heap size)
(97 MB heap size)
(107 MB heap size)
(108 MB heap size)
(109 MB heap size)
(118 MB heap size)
(120 MB heap size)
(121 MB heap size)
(130 MB heap size)
(132 MB heap size)
(133 MB heap size)
(143 MB heap size)
(144 MB heap size)
(145 MB heap size)
(154 MB heap size)
(156 MB heap size)
(157 MB heap size)
(166 MB heap size)
(168 MB heap size)
(169 MB heap size)
(179 MB heap size)
(181 MB heap size)
(182 MB heap size)
(191 MB heap size)
(193 MB heap size)
(194 MB heap size)
(203 MB heap size)
(205 MB heap size)
(207 MB heap size)
(216 MB heap size)
(217 MB heap size)
(219 MB heap size)
(228 MB heap size)
(230 MB heap size)
(231 MB heap size)
(240 MB heap size)
(242 MB heap size)
(243 MB heap size)
(252 MB heap size)
(254 MB heap size)
(255 MB heap size)
(264 MB heap size)
(266 MB heap size)
(267 MB heap size)
(277 MB heap size)
(278 MB heap size)
(280 MB heap size)
(195 MB heap size)
(204 MB heap size)
(203 MB heap size)
(212 MB heap size)
(213 MB heap size)
(214 MB heap size)
(223 MB heap size)
(224 MB heap size)
(226 MB heap size)
(235 MB heap size)
(237 MB heap size)
(238 MB heap size)
(247 MB heap size)
(249 MB heap size)
(250 MB heap size)
(259 MB heap size)
(261 MB heap size)
(262 MB heap size)
(271 MB heap size)
(273 MB heap size)
(274 MB heap size)
(283 MB heap size)

Test Suites: 100 passed, 100 total
Tests:       1000 passed, 1000 total
Snapshots:   0 total
Time:        11.347 s, estimated 12 s

解消方法

npm i -D @side/jest-runtime などで@side/jest-runtimeを導入し、jest.config.jsに以下の行を追加することで改善します。

  runtime: '@side/jest-runtime',

このコードで何か既存の実装やテストに影響が発生するかどうかは確認していませんが、後述する@side/jest-runtimeが生まれる切欠になったPRの様子を見る限り大丈夫なんじゃないかなとなんとなく思っています。

メモリリークが改善したあとの様子

(39 MB heap size)
(39 MB heap size)
(47 MB heap size)
(47 MB heap size)
(34 MB heap size)
(42 MB heap size)
(41 MB heap size)
(49 MB heap size)
(51 MB heap size)
(59 MB heap size)
(59 MB heap size)
(60 MB heap size)
(68 MB heap size)
(69 MB heap size)
(77 MB heap size)
(77 MB heap size)
(85 MB heap size)
(86 MB heap size)
(95 MB heap size)
(95 MB heap size)
(95 MB heap size)
(103 MB heap size)
(104 MB heap size)
(112 MB heap size)
(112 MB heap size)
(120 MB heap size)
(121 MB heap size)
(31 MB heap size)
(38 MB heap size)
(37 MB heap size)
(44 MB heap size)
(46 MB heap size)
(54 MB heap size)
(54 MB heap size)
(54 MB heap size)
(62 MB heap size)
(62 MB heap size)
(70 MB heap size)
(71 MB heap size)
(79 MB heap size)
(79 MB heap size)
(87 MB heap size)
(88 MB heap size)
(96 MB heap size)
(96 MB heap size)
(97 MB heap size)
(105 MB heap size)
(105 MB heap size)
(31 MB heap size)
(39 MB heap size)
(37 MB heap size)
(44 MB heap size)
(46 MB heap size)
(54 MB heap size)
(54 MB heap size)
(54 MB heap size)
(62 MB heap size)
(62 MB heap size)
(70 MB heap size)
(70 MB heap size)
(78 MB heap size)
(79 MB heap size)
(87 MB heap size)
(88 MB heap size)
(96 MB heap size)
(96 MB heap size)
(96 MB heap size)
(104 MB heap size)
(105 MB heap size)
(31 MB heap size)
(39 MB heap size)
(37 MB heap size)
(45 MB heap size)
(46 MB heap size)
(54 MB heap size)
(54 MB heap size)
(54 MB heap size)
(62 MB heap size)
(63 MB heap size)
(70 MB heap size)
(71 MB heap size)
(78 MB heap size)
(79 MB heap size)
(87 MB heap size)
(88 MB heap size)
(96 MB heap size)
(96 MB heap size)
(97 MB heap size)
(105 MB heap size)
(105 MB heap size)
(30 MB heap size)
(37 MB heap size)
(45 MB heap size)
(43 MB heap size)
(44 MB heap size)
(51 MB heap size)
(51 MB heap size)
(59 MB heap size)
(59 MB heap size)
(67 MB heap size)

Test Suites: 100 passed, 100 total
Tests:       1000 passed, 1000 total
Snapshots:   0 total
Time:        9.071 s, estimated 11 s