bug: fs.readdirSync with recursive option not working

[benhovinga]

The recursive option on fs.readdirSync is not working as expected when using mock-fs.

version: "mock-fs": "^5.5.0"

Failing test with mock-fs

This test should pass but it doesn't.

import { expect, test } from '@jest/globals';
import fs from 'fs';
import mockFS from 'mock-fs';

beforeEach(function () {
  mockFS({
    'path/to/example': {
      'file1.txt': 'file contents',
      dir: {
        'file2.txt': 'file contents',
        subdir: {
          'file3.txt': 'file contents'
        }
      }
    }
  });
});

afterEach(mockFS.restore);

test.only('get mocked files', () => {
  const files = fs.readdirSync('./path/to/example/', {
    recursive: true
  });
  expect(files).toEqual([
    'dir',
    'file1.txt',
    'dir/file2.txt',
    'dir/subdir',
    'dir/subdir/file3.txt'
  ]);
});

Test results:

> jest "test/test.spec.ts"

 FAIL  test/test.spec.ts
  ✕ get mocked files (3 ms)

  ● get mocked files

    expect(received).toEqual(expected) // deep equality

    - Expected  - 3
    + Received  + 0

      Array [
        "dir",
        "file1.txt",
    -   "dir/file2.txt",
    -   "dir/subdir",
    -   "dir/subdir/file3.txt",
      ]

      23 |     recursive: true
      24 |   });
    > 25 |   expect(files).toEqual([
         |                 ^
      26 |     'dir',
      27 |     'file1.txt',
      28 |     'dir/file2.txt',

      at Object.<anonymous> (test/test.spec.ts:25:17)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        0.117 s, estimated 1 s
Ran all test suites matching /test\/test.spec.ts/i.
 ELIFECYCLE  Test failed. See above for more details.

Passing test with fs

I commented out the mock-fs configuration and I created the same directory structure on my system. I ran the test again and I got the the test passed. So we know fs.readdirSync is working.

- ./path/to/example/
   - file1.txt
   - dir/
      - file2.txt
      - subdir/
         - file3.txt

import { expect, test } from '@jest/globals';
import fs from 'fs';
// import mockFS from 'mock-fs';

// beforeEach(function () {
//   mockFS({
//     'path/to/example': {
//       'file1.txt': 'file contents',
//       dir: {
//         'file2.txt': 'file contents',
//         subdir: {
//           'file3.txt': 'file contents'
//         }
//       }
//     }
//   });
// });

// afterEach(mockFS.restore);

test.only('get mocked files', () => {
  const files = fs.readdirSync('./path/to/example/', {
    recursive: true
  });
  expect(files).toEqual([
    'dir',
    'file1.txt',
    'dir/file2.txt',
    'dir/subdir',
    'dir/subdir/file3.txt'
  ]);
});

Test results:

> jest "test/test.spec.ts"

 PASS  test/test.spec.ts
  ✓ get mocked files (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.095 s, estimated 1 s
Ran all test suites matching /test\/test.spec.ts/i.

Its a trap!

After testing the native fs I removed the comments to re-enable mock-fs and now the test is passing with mocks. As it turns out it is still looking into the ./path/to/example/ directory I created on my filesystem.

It looks like mock-fs is still adding the mocked files into the list and fs merges any remaining on top.

If I add another file to the mock path at this point it fails with 1 extra file in the list.

  mockFS({
    'path/to/example': {
      'file1.txt': 'file contents',
      dir: {
        'file2.txt': 'file contents',
        subdir: {
          'file3.txt': 'file contents',
          'file4.txt': 'file contents'  // <-- Extra
        }
      }
    }
  });

> jest "test/test.spec.ts"

 FAIL  test/test.spec.ts
  ✕ get mocked files (4 ms)

  ● get mocked files

    expect(received).toEqual(expected) // deep equality

    - Expected  - 0
    + Received  + 1

    @@ -2,6 +2,7 @@
        "dir",
        "file1.txt",
        "dir/file2.txt",
        "dir/subdir",
        "dir/subdir/file3.txt",
    +   "dir/subdir/file4.txt",
      ]

      24 |     recursive: true
      25 |   });
    > 26 |   expect(files).toEqual([
         |                 ^
      27 |     'dir',
      28 |     'file1.txt',
      29 |     'dir/file2.txt',

      at Object.<anonymous> (test/test.spec.ts:26:17)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        0.137 s, estimated 1 s
Ran all test suites matching /test\/test.spec.ts/i.
 ELIFECYCLE  Test failed. See above for more details.

But if I remove the directory from my filesystem it goes back to missing all of the recursive directories again and doesn't show the extra file4.txt I added above.

> jest "test/test.spec.ts"

 FAIL  test/test.spec.ts
  ✕ get mocked files (3 ms)

  ● get mocked files

    expect(received).toEqual(expected) // deep equality

    - Expected  - 3
    + Received  + 0

      Array [
        "dir",
        "file1.txt",
    -   "dir/file2.txt",
    -   "dir/subdir",
    -   "dir/subdir/file3.txt",
      ]

      24 |     recursive: true
      25 |   });
    > 26 |   expect(files).toEqual([
         |                 ^
      27 |     'dir',
      28 |     'file1.txt',
      29 |     'dir/file2.txt',

      at Object.<anonymous> (test/test.spec.ts:26:17)

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        0.119 s, estimated 1 s
Ran all test suites matching /test\/test.spec.ts/i.
 ELIFECYCLE  Test failed. See above for more details.