easy_mock_io

In-memory dart:io for Flutter tests. mockMemoryIO.init() replaces IOOverrides.global with a MemoryFileSystem, so every File / Directory your code under test touches runs in memory instead of hitting the real disk — no temp files to clean up, and tests stay isolated from each other.

Usage

import 'dart:io';

import 'package:easy_mock_io/easy_mock_io.dart';
import 'package:flutter_test/flutter_test.dart';

setUp(() => mockMemoryIO.init());
tearDown(() => IOOverrides.global = null);

test('writes go to memory, not disk', () {
  File('/notes/todo.txt')
    ..createSync(recursive: true)
    ..writeAsStringSync('hi');

  expect(File('/notes/todo.txt').readAsStringSync(), 'hi');
});

• mockMemoryIO.init([MemoryFileSystem? fs, MemoryIOConfig config]) installs the override. Pass a pre-seeded filesystem to start with files already present; omit it for a fresh one with the default directories. config controls the asset seeding and root path. Existing files in a supplied filesystem are kept when the directory layout is created.
• File locks are no-ops. lock / unlock (sync and async) return immediately, so tests that open the same path in parallel can't deadlock on an exclusive lock the memory filesystem wouldn't honour anyway.
• Assets are seeded from the folder named by the UNIT_TEST_ASSETS environment variable and from MemoryIOConfig.testAssetsDirPath (test/assets by default).

init sets IOOverrides.global; reset it with IOOverrides.global = null in tearDown (or install a fresh one per test) so overrides don't leak.

Default directories

init() pre-creates this application directory layout in memory:

Under external/files, the music, podcasts, ringtones, alarms, notifications, pictures, movies, downloads, dcim, and documents subdirectories are also created for common external-storage categories.

Files can be written directly into these directories without creating parents:

mockMemoryIO.init();
File('/app_root/documents/settings.json').writeAsStringSync('{}');

Setting MemoryIOConfig(rootDirPath: '/custom/app') creates the same layout under /custom/app. Custom directories outside the pre-created layout must be created by your test or pre-seeded filesystem.