IOOverrides using package:file for testing (#4774)

pubspec.lock

diff --git a/pubspec.lock b/pubspec.lock
index c7bc53a..4d9ed0f 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -106,7 +106,7 @@
     source: hosted
     version: "3.5.2"
   file:
-    dependency: transitive
+    dependency: "direct dev"
     description:
       name: file
       sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index ab0f64d..54973d2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -33,6 +33,7 @@
 dev_dependencies:
   checks: ^0.3.1
   dart_flutter_team_lints: ^3.5.2
+  file: ^7.0.1
   shelf_test_handler: ^2.0.2
   test: ^1.26.3
   test_descriptor: ^2.0.2

test/wasm/iooverrides.dart

diff --git a/test/wasm/iooverrides.dart b/test/wasm/iooverrides.dart
new file mode 100644
index 0000000..4532703
--- /dev/null
+++ b/test/wasm/iooverrides.dart
@@ -0,0 +1,56 @@
+import 'dart:io';
+
+import 'package:file/file.dart' as f;
+
+/// Creates an [IOOverrides] that uses [fs] for all operations.
+IOOverrides createFileSystemIOOverrides(f.FileSystem fs) =>
+    _FileSystemIOOverrides(fs);
+
+/// An [IOOverrides] that uses a [f.FileSystem] for all operations.
+final class _FileSystemIOOverrides extends IOOverrides {
+  final f.FileSystem _fs;
+
+  _FileSystemIOOverrides(this._fs);
+
+  @override
+  File createFile(String path) => _fs.file(path);
+
+  @override
+  Directory createDirectory(String path) => _fs.directory(path);
+
+  @override
+  Link createLink(String path) => _fs.link(path);
+
+  @override
+  Future<FileStat> stat(String path) => _fs.stat(path);
+
+  @override
+  FileStat statSync(String path) => _fs.statSync(path);
+
+  @override
+  Future<bool> fseIdentical(String path1, String path2) =>
+      _fs.identical(path1, path2);
+
+  @override
+  bool fseIdenticalSync(String path1, String path2) =>
+      _fs.identicalSync(path1, path2);
+
+  @override
+  Future<FileSystemEntityType> fseGetType(String path, bool followLinks) =>
+      _fs.type(path, followLinks: followLinks);
+
+  @override
+  FileSystemEntityType fseGetTypeSync(String path, bool followLinks) =>
+      _fs.typeSync(path, followLinks: followLinks);
+
+  @override
+  Directory getCurrentDirectory() => _fs.currentDirectory;
+
+  @override
+  void setCurrentDirectory(String path) {
+    _fs.currentDirectory = path;
+  }
+
+  @override
+  Directory getSystemTempDirectory() => _fs.systemTempDirectory;
+}

test/wasm/iooverrides_test.dart

diff --git a/test/wasm/iooverrides_test.dart b/test/wasm/iooverrides_test.dart
new file mode 100644
index 0000000..0986462
--- /dev/null
+++ b/test/wasm/iooverrides_test.dart
@@ -0,0 +1,44 @@
+import 'dart:io';
+
+import 'package:file/memory.dart';
+import 'package:test/test.dart';
+
+import 'iooverrides.dart';
+
+void main() {
+  test('FileSystemIOOverrides redirects IO operations', () async {
+    final fs = MemoryFileSystem();
+    await IOOverrides.runWithIOOverrides(() async {
+      final file = File('/test.txt');
+      await file.writeAsString('hello');
+
+      expect(fs.file('/test.txt').readAsStringSync(), 'hello');
+      expect(await file.readAsString(), 'hello');
+
+      final dir = Directory('/subdir');
+      await dir.create();
+      expect(fs.directory('/subdir').existsSync(), isTrue);
+
+      final list = await Directory('/').list().toList();
+      expect(list.map((e) => e.path), containsAll(['test.txt', 'subdir']));
+    }, createFileSystemIOOverrides(fs));
+  });
+
+  test('getCurrentDirectory and setCurrentDirectory', () async {
+    final fs = MemoryFileSystem();
+    fs.directory('/a/b').createSync(recursive: true);
+    await IOOverrides.runWithIOOverrides(() async {
+      expect(Directory.current.path, '/');
+      Directory.current = '/a/b';
+      expect(Directory.current.path, '/a/b');
+      expect(fs.currentDirectory.path, '/a/b');
+    }, createFileSystemIOOverrides(fs));
+  });
+
+  test('systemTempDirectory', () async {
+    final fs = MemoryFileSystem();
+    await IOOverrides.runWithIOOverrides(() async {
+      expect(Directory.systemTemp.path, fs.systemTempDirectory.path);
+    }, createFileSystemIOOverrides(fs));
+  });
+}