[CLI tool] in flutter test, consider --flavor when validating the cached asset bundle (#150461)

Fixes flutter/flutter#150296

**Context.** `flutter test` has its own code path for writing flutter app [assets](https://docs.flutter.dev/ui/assets/assets-and-images). flutter/flutter#132985 introduced [flavor-conditional asset bundling ](https://docs.flutter.dev/deployment/flavors#conditionally-bundling-assets-based-on-flavor), which lets users control which assets get bundled based on `--flavor`. `--flavor` is supported in `flutter test`.

**Bug and fix.** `--flavor` isn't considered when deciding whether we need to rebuild this asset bundle:

https://github.com/flutter/flutter/blob/5e448f4ce57723ac0792ae822ebac69df3188ba1/packages/flutter_tools/lib/src/commands/test.dart#L709

This PR address this by writing the value of `--flavor` to a file in the build directory and checking that when validating the cached asset bundle.

Author: andrewkolos

packages/flutter_tools/lib/src/commands/test.dart

@@ -695,7 +695,7 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
     if (build != 0) {
       throwToolExit('Error: Failed to build asset bundle');
     }
-    if (_needRebuild(assetBundle.entries)) {
+    if (_needsRebuild(assetBundle.entries, flavor)) {
       await writeBundle(
         globals.fs.directory(globals.fs.path.join('build', 'unit_test_assets')),
         assetBundle.entries,
@@ -708,14 +708,25 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
         projectDir: globals.fs.currentDirectory,
         buildMode: buildMode,
       );
+
+      final File cachedFlavorFile = globals.fs.file(
+        globals.fs.path.join('build', 'test_cache', 'flavor.txt'),
+      );
+      if (cachedFlavorFile.existsSync()) {
+        await cachedFlavorFile.delete();
+      }
+      if (flavor != null) {
+        cachedFlavorFile.createSync(recursive: true);
+        cachedFlavorFile.writeAsStringSync(flavor);
+      }
     }
   }
 
-  bool _needRebuild(Map<String, AssetBundleEntry> entries) {
+  bool _needsRebuild(Map<String, AssetBundleEntry> entries, String? flavor) {
     // TODO(andrewkolos): This logic might fail in the future if we change the
-    // schema of the contents of the asset manifest file and the user does not
-    // perform a `flutter clean` after upgrading.
-    // See https://github.com/flutter/flutter/issues/128563.
+    //  schema of the contents of the asset manifest file and the user does not
+    //  perform a `flutter clean` after upgrading.
+    //  See https://github.com/flutter/flutter/issues/128563.
     final File manifest = globals.fs.file(globals.fs.path.join('build', 'unit_test_assets', 'AssetManifest.bin'));
     if (!manifest.existsSync()) {
       return true;
@@ -736,6 +747,17 @@ class TestCommand extends FlutterCommand with DeviceBasedDevelopmentArtifacts {
         return true;
       }
     }
+
+    final File cachedFlavorFile = globals.fs.file(
+      globals.fs.path.join('build', 'test_cache', 'flavor.txt'),
+    );
+    final String? cachedFlavor = cachedFlavorFile.existsSync()
+        ? cachedFlavorFile.readAsStringSync()
+        : null;
+    if (cachedFlavor != flavor) {
+      return true;
+    }
+
     return false;
   }
 }

packages/flutter_tools/test/commands.shard/hermetic/test_test.dart

@@ -7,6 +7,7 @@ import 'dart:convert';
 
 import 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
+import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/async_guard.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -1178,6 +1179,59 @@ dev_dependencies:
     DeviceManager: () => _FakeDeviceManager(<Device>[]),
   });
 
+  testUsingContext('correctly considers --flavor when validating the cached asset bundle', () async {
+    final FakeFlutterTestRunner testRunner = FakeFlutterTestRunner(0);
+    fs.file('vanilla.txt').writeAsStringSync('vanilla');
+    fs.file('flavorless.txt').writeAsStringSync('flavorless');
+    fs.file('pubspec.yaml').writeAsStringSync('''
+flutter:
+  assets:
+    - path: vanilla.txt
+      flavors:
+        - vanilla
+    - flavorless.txt
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  integration_test:
+    sdk: flutter''');
+    final TestCommand testCommand = TestCommand(testRunner: testRunner);
+    final CommandRunner<void> commandRunner = createTestCommandRunner(testCommand);
+
+    const List<String> buildArgsFlavorless = <String>[
+      'test',
+      '--no-pub',
+    ];
+
+    const List<String> buildArgsVanilla = <String>[
+      'test',
+      '--no-pub',
+      '--flavor',
+      'vanilla',
+    ];
+
+    final File builtVanillaAssetFile = fs.file(
+      fs.path.join('build', 'unit_test_assets', 'vanilla.txt'),
+    );
+    final File builtFlavorlessAssetFile = fs.file(
+      fs.path.join('build', 'unit_test_assets', 'flavorless.txt'),
+    );
+
+    await commandRunner.run(buildArgsVanilla);
+    await commandRunner.run(buildArgsFlavorless);
+
+    expect(builtVanillaAssetFile, isNot(exists));
+    expect(builtFlavorlessAssetFile, exists);
+
+    await commandRunner.run(buildArgsVanilla);
+
+    expect(builtVanillaAssetFile, exists);
+  }, overrides: <Type, Generator>{
+    FileSystem: () => fs,
+    ProcessManager: () => FakeProcessManager.empty(),
+    DeviceManager: () => _FakeDeviceManager(<Device>[]),
+  });
+
   testUsingContext("Don't build the asset manifest if --no-test-assets if informed", () async {
     final FakeFlutterTestRunner testRunner = FakeFlutterTestRunner(0);