[flutter_conductor] Refactor next command (#91768)

dev/conductor/core/lib/src/next.dart

@@ -4,12 +4,12 @@
 
 import 'package:args/command_runner.dart';
 import 'package:file/file.dart' show File;
-import 'package:meta/meta.dart' show visibleForTesting;
+import 'package:meta/meta.dart' show visibleForTesting, visibleForOverriding;
 import './globals.dart';
 import './proto/conductor_state.pb.dart' as pb;
 import './proto/conductor_state.pbenum.dart';
 import './repository.dart';
-import './state.dart';
+import './state.dart' as state_import;
 import './stdio.dart';
 
 const String kStateOption = 'state-file';
@@ -21,7 +21,7 @@ class NextCommand extends Command<void> {
   NextCommand({
     required this.checkouts,
   }) {
-    final String defaultPath = defaultStateFilePath(checkouts.platform);
+    final String defaultPath = state_import.defaultStateFilePath(checkouts.platform);
     argParser.addOption(
       kStateOption,
       defaultsTo: defaultPath,
@@ -48,38 +48,33 @@ class NextCommand extends Command<void> {
 
   @override
   Future<void> run() async {
-    await runNext(
+    await NextContext(
       autoAccept: argResults![kYesFlag] as bool,
       checkouts: checkouts,
       force: argResults![kForceFlag] as bool,
       stateFile: checkouts.fileSystem.file(argResults![kStateOption]),
-    );
+    ).run();
   }
 }
 
-@visibleForTesting
-bool prompt(String message, Stdio stdio) {
-  stdio.write('${message.trim()} (y/n) ');
-  final String response = stdio.readLineSync().trim();
-  final String firstChar = response[0].toUpperCase();
-  if (firstChar == 'Y') {
-    return true;
-  }
-  if (firstChar == 'N') {
-    return false;
-  }
-  throw ConductorException(
-    'Unknown user input (expected "y" or "n"): $response',
-  );
-}
+/// Utility class for proceeding to the next step in a release.
+///
+/// Any calls to functions that cause side effects are wrapped in methods to
+/// allow overriding in unit tests.
+class NextContext {
+  NextContext({
+    required this.autoAccept,
+    required this.force,
+    required this.checkouts,
+    required this.stateFile,
+  });
+
+  final bool autoAccept;
+  final bool force;
+  final Checkouts checkouts;
+  final File stateFile;
 
-@visibleForTesting
-Future<void> runNext({
-  required bool autoAccept,
-  required bool force,
-  required Checkouts checkouts,
-  required File stateFile,
-}) async {
+  Future<void> run() async {
     final Stdio stdio = checkouts.stdio;
     const List<CherrypickState> finishedStates = <CherrypickState>[
       CherrypickState.COMPLETED,
@@ -121,7 +116,7 @@ Future<void> runNext({
           ));
         }
 
-      if (!requiresEnginePR(state)) {
+        if (!state_import.requiresEnginePR(state)) {
           stdio.printStatus(
               'This release has no engine cherrypicks. No Engine PR is necessary.\n',
           );
@@ -390,10 +385,37 @@ Future<void> runNext({
       case pb.ReleasePhase.RELEASE_COMPLETED:
         throw ConductorException('This release is finished.');
     }
-  final ReleasePhase nextPhase = getNextPhase(state.currentPhase);
+    final ReleasePhase nextPhase = state_import.getNextPhase(state.currentPhase);
     stdio.printStatus('\nUpdating phase from ${state.currentPhase} to $nextPhase...\n');
     state.currentPhase = nextPhase;
-  stdio.printStatus(phaseInstructions(state));
+    stdio.printStatus(state_import.phaseInstructions(state));
 
     writeStateToFile(stateFile, state, stdio.logs);
+  }
+
+  /// Persist the state to a file.
+  @visibleForOverriding
+  void writeStateToFile(File file, pb.ConductorState state, [List<String> logs = const <String>[]]) {
+    state_import.writeStateToFile(file, state, logs);
+  }
+
+  @visibleForTesting
+  bool prompt(String message, Stdio stdio) {
+    stdio.write('${message.trim()} (y/n) ');
+    final String response = stdio.readLineSync().trim();
+    final String firstChar = response[0].toUpperCase();
+    if (firstChar == 'Y') {
+      return true;
+    }
+    if (firstChar == 'N') {
+      return false;
+    }
+    throw ConductorException(
+      'Unknown user input (expected "y" or "n"): $response',
+    );
+  }
+
+  /// Read the state from a file.
+  @visibleForOverriding
+  pb.ConductorState readStateFromFile(File file) => state_import.readStateFromFile(file);
 }

dev/conductor/core/test/next_test.dart

@@ -1052,6 +1052,34 @@ void main() {
   }, onPlatform: <String, dynamic>{
     'windows': const Skip('Flutter Conductor only supported on macos/linux'),
   });
+
+  group('prompt', () {
+    test('throws if user inputs character that is not "y" or "n"', () {
+      final FileSystem fileSystem = MemoryFileSystem.test();
+      final TestStdio stdio = TestStdio(
+        stdin: <String>['x'],
+        verbose: true,
+      );
+      final Checkouts checkouts = Checkouts(
+        fileSystem: fileSystem,
+        parentDirectory: fileSystem.directory('/'),
+        platform: FakePlatform(),
+        processManager: FakeProcessManager.empty(),
+        stdio: stdio,
+      );
+      final NextContext context = NextContext(
+        autoAccept: false,
+        force: false,
+        checkouts: checkouts,
+        stateFile: fileSystem.file('/statefile.json'),
+      );
+
+      expect(
+        () => context.prompt('Asking a question?', stdio),
+        throwsExceptionWith('Unknown user input (expected "y" or "n")'),
+      );
+    });
+  });
 }
 
 void _initializeCiYamlFile(