Fix for issue 21771

pkg/analyzer/test/generated/resolver_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library engine.resolver_test;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 7023 matching lines @@
   E e;
   m() {
     (e as A).a();
   }
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
+  void test_unnecessaryCast_conditionalExpression() {
+    Source source = addSource(r'''
+abstract class I {}
+class A implements I {}
+class B implements I {}
+I m(A a, B b) {
+  return a == null ? b as I : a as I;
+}''');
+    resolve(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   void test_unnecessaryCast_dynamic_type() {
     Source source = addSource(r'''
 m(v) {
   var b = v as Object;
 }''');
     resolve(source);
     assertNoErrors(source);
     verify([source]);
   }
 
@@ skipping 6747 matching lines @@
         // check propagated type
         FunctionType propagatedType = node.propagatedType as FunctionType;
         expect(propagatedType.returnType, test.typeProvider.stringType);
       } on AnalysisException catch (e, stackTrace) {
         thrownException[0] = new CaughtException(e, stackTrace);
       }
     }
     return null;
   }
 }