test: Verify assertion for null TextDirection in AlignmentDirectional

Adds a test case to ensure that calling `AlignmentDirectional.resolve` with a null `TextDirection` throws a `FlutterError` with the expected improved message.
flutter · auto-submit · Jul 22, 2025 · Jul 14, 2025 · Jul 14, 2025 · Jul 14, 2025
commit bffcfba974fe61ac1cc51e5e59e357c7e7669936
diff --git a/packages/flutter/test/painting/alignment_test.dart b/packages/flutter/test/painting/alignment_test.dart
@@ -4,6 +4,7 @@
 
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -350,4 +351,21 @@ void main() {
     expect(AlignmentGeometry.bottomCenter, Alignment.bottomCenter);
     expect(AlignmentGeometry.bottomRight, Alignment.bottomRight);
   });
+
+  test('AlignmentDirectional.resolve with null TextDirection asserts', () {
+    const AlignmentDirectional alignmentDirectional = AlignmentDirectional(1.0, 2.0);
+
+    expect(
+      () => alignmentDirectional.resolve(null),
+      throwsA(
+        isFlutterError.having(
+          (FlutterError e) => e.message,
+          'message',
+          allOf(contains('No TextDirection found.'), contains('without a Directionality ancestor')),
+        ),
+      ),
+    );
+  });
 }
+
+double nonconst(double value) => value;