adds check if the TerminalIsolate has already been started

and throws an exception when it is not

example/lib/isolate.dart

@@ -91,10 +91,11 @@ class _MyHomePageState extends State<MyHomePage> {
     maxLines: 10000,
   );
 
-  @override
-  void initState() {
-    super.initState();
-    terminal.start();
+  Future<TerminalIsolate> _ensureTerminalStarted() async {
+    if (!terminal.isReady) {
+      await terminal.start();
+    }
+    return terminal;
   }
 
   void onInput(String input) {}
@@ -102,8 +103,15 @@ class _MyHomePageState extends State<MyHomePage> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      body: SafeArea(
-        child: TerminalView(terminal: terminal),
+      body: FutureBuilder(
+        future: _ensureTerminalStarted(),
+        builder: (context, snapshot) {
+          return SafeArea(
+            child: snapshot.hasData
+                ? TerminalView(terminal: snapshot.data as TerminalIsolate)
+                : Text('Initializing...'),
+          );
+        },
       ),
     );
   }

lib/terminal/terminal_isolate.dart

@@ -286,6 +286,7 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   final _receivePort = ReceivePort();
   SendPort? _sendPort;
   late Isolate _isolate;
+  bool _isStarted = false;
 
   final TerminalBackend? backend;
   final BellHandler onBell;
@@ -319,28 +320,50 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
         _refreshEventDebouncer = EventDebouncer(minRefreshDelay);
 
   @override
-  int get scrollOffsetFromBottom => _lastState!.scrollOffsetFromBottom;
+  int get scrollOffsetFromBottom {
+    _assertStarted();
+    return _lastState!.scrollOffsetFromBottom;
+  }
 
   @override
-  int get scrollOffsetFromTop => _lastState!.scrollOffsetFromTop;
+  int get scrollOffsetFromTop {
+    _assertStarted();
+    return _lastState!.scrollOffsetFromTop;
+  }
 
   @override
-  int get bufferHeight => _lastState!.bufferHeight;
+  int get bufferHeight {
+    _assertStarted();
+    return _lastState!.bufferHeight;
+  }
 
   @override
-  int get terminalHeight => _lastState!.viewHeight;
+  int get terminalHeight {
+    _assertStarted();
+    return _lastState!.viewHeight;
+  }
 
   @override
-  int get terminalWidth => _lastState!.viewWidth;
+  int get terminalWidth {
+    _assertStarted();
+    return _lastState!.viewWidth;
+  }
 
   @override
-  int get invisibleHeight => _lastState!.invisibleHeight;
+  int get invisibleHeight {
+    _assertStarted();
+    return _lastState!.invisibleHeight;
+  }
 
   @override
-  Selection? get selection => _lastState?.selection;
+  Selection? get selection {
+    return _lastState?.selection;
+  }
 
   @override
-  bool get showCursor => _lastState?.showCursor ?? true;
+  bool get showCursor {
+    return _lastState?.showCursor ?? true;
+  }
 
   @override
   List<BufferLine> getVisibleLines() {
@@ -351,10 +374,14 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   }
 
   @override
-  int get cursorY => _lastState?.cursorY ?? 0;
+  int get cursorY {
+    return _lastState?.cursorY ?? 0;
+  }
 
   @override
-  int get cursorX => _lastState?.cursorX ?? 0;
+  int get cursorX {
+    return _lastState?.cursorX ?? 0;
+  }
 
   @override
   BufferLine? get currentLine {
@@ -371,10 +398,14 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   }
 
   @override
-  int get cursorColor => _lastState?.cursorColor ?? 0;
+  int get cursorColor {
+    return _lastState?.cursorColor ?? 0;
+  }
 
   @override
-  int get backgroundColor => _lastState?.backgroundColor ?? 0;
+  int get backgroundColor {
+    return _lastState?.backgroundColor ?? 0;
+  }
 
   @override
   bool get dirty {
@@ -392,12 +423,14 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   PlatformBehavior get platform => _platform;
 
   @override
-  String? get selectedText => _lastState?.selectedText;
+  String? get selectedText {
+    return _lastState?.selectedText;
+  }
 
   @override
   bool get isReady => _lastState != null;
 
-  Future<void> start() async {
+  Future<void> start({bool testingDontWaitForBootup = false}) async {
     final initialRefreshCompleted = Completer<bool>();
     var firstReceivePort = ReceivePort();
     _isolate = await Isolate.spawn(terminalMain, firstReceivePort.sendPort);
@@ -438,10 +471,14 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
       _IsolateCommand.init,
       TerminalInitData(this.backend, this.platform, this.theme, this.maxLines)
     ]);
-    await initialRefreshCompleted.future;
+    if (!testingDontWaitForBootup) {
+      await initialRefreshCompleted.future;
+    }
+    _isStarted = true;
   }
 
   void stop() {
+    _assertStarted();
     terminateBackend();
     _isolate.kill();
   }
@@ -562,7 +599,9 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   bool get isTerminated => _isTerminated;
 
   @override
-  String get composingString => _lastState?.composingString ?? '';
+  String get composingString {
+    return _lastState?.composingString ?? '';
+  }
 
   @override
   void updateComposingString(String value) {
@@ -574,10 +613,14 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
       _lastState?.searchResult ?? TerminalSearchResult.empty();
 
   @override
-  int get numberOfSearchHits => userSearchResult.allHits.length;
+  int get numberOfSearchHits {
+    return userSearchResult.allHits.length;
+  }
 
   @override
-  int? get currentSearchHit => userSearchResult.currentSearchHit;
+  int? get currentSearchHit {
+    return userSearchResult.currentSearchHit;
+  }
 
   @override
   void set currentSearchHit(int? currentSearchHit) {
@@ -594,7 +637,9 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   }
 
   @override
-  String? get userSearchPattern => _lastState?.userSearchPattern;
+  String? get userSearchPattern {
+    return _lastState?.userSearchPattern;
+  }
 
   @override
   void set userSearchPattern(String? newValue) {
@@ -602,11 +647,20 @@ class TerminalIsolate with Observable implements TerminalUiInteraction {
   }
 
   @override
-  bool get isUserSearchActive => _lastState?.isUserSearchActive ?? false;
+  bool get isUserSearchActive {
+    return _lastState?.isUserSearchActive ?? false;
+  }
 
   @override
   void set isUserSearchActive(bool isUserSearchActive) {
     _sendPort
         ?.send([_IsolateCommand.updateIsUserSearchActive, isUserSearchActive]);
   }
+
+  void _assertStarted() {
+    if (!_isStarted) {
+      throw Exception(
+          'Ther Terminal Isolate has to be started before using it! (call await terminalIsolate.start()');
+    }
+  }
 }

test/terminal/terminal_isolate_test.dart

@@ -0,0 +1,86 @@
+import 'dart:async';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:xterm/terminal/terminal_backend.dart';
+import 'package:xterm/terminal/terminal_isolate.dart';
+
+void main() {
+  group('Start behavior tests', () {
+    test('Using TerminalIsolate when not started throws exception', () {
+      final fixture = _TestFixture();
+      expect(() => fixture.uut.terminalWidth, throwsA(isA<Exception>()));
+    });
+    test('Using TerminalIsolate after started doesn\'t throw exceptions',
+        () async {
+      final fixture = _TestFixture();
+
+      await fixture.uut.start(testingDontWaitForBootup: true);
+
+      //no throw
+      fixture.uut.showCursor;
+    });
+  });
+}
+
+class _TestFixture {
+  _TestFixture() {
+    fakeBackend = FakeBackend();
+    uut = TerminalIsolate(maxLines: 10000, backend: fakeBackend);
+  }
+
+  late final TerminalIsolate uut;
+  late final FakeBackend fakeBackend;
+}
+
+class FakeBackend implements TerminalBackend {
+  @override
+  void ackProcessed() {}
+
+  @override
+  // TODO: implement exitCode
+  Future<int> get exitCode => _exitCodeCompleter.future;
+
+  @override
+  void init() {
+    _exitCodeCompleter = Completer<int>();
+    _outStream = StreamController<String>();
+    _hasInitBeenCalled = true;
+  }
+
+  @override
+  Stream<String> get out => _outStream.stream;
+
+  @override
+  void resize(int width, int height, int pixelWidth, int pixelHeight) {
+    _width = width;
+    _height = height;
+    _pixelWidth = pixelWidth;
+    _pixelHeight = pixelHeight;
+  }
+
+  @override
+  void terminate() {
+    _isTerminated = true;
+  }
+
+  @override
+  void write(String _) {}
+
+  bool get hasInitBeenCalled => _hasInitBeenCalled;
+  bool get isTerminated => _isTerminated;
+
+  int? get width => _width;
+  int? get height => _height;
+  int? get pixelWidth => _pixelWidth;
+  int? get pixelHeight => _pixelHeight;
+
+  bool _hasInitBeenCalled = false;
+  bool _isTerminated = false;
+  int? _width;
+  int? _height;
+  int? _pixelWidth;
+  int? _pixelHeight;
+
+  late final _exitCodeCompleter;
+  late final _outStream;
+}

test/terminal/terminal_search_test.dart

@@ -1,5 +1,3 @@
-import 'dart:developer';
-
 import 'package:flutter_test/flutter_test.dart';
 import 'package:mockito/annotations.dart';
 import 'package:mockito/mockito.dart';