remove duplicate suggestions

pkg/analysis_services/test/completion/completion_test_util.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 test.services.completion.util;
 
 import 'dart:async';
 
 import 'package:analysis_services/completion/completion_computer.dart';
 import 'package:analysis_services/completion/completion_suggestion.dart';
@@ skipping 37 matching lines @@
 
   void assertNotSuggested(String completion) {
     if (suggestions.any((cs) => cs.completion == completion)) {
       fail('did not expect completion: $completion');
     }
   }
 
   void assertSuggest(CompletionSuggestionKind kind, String completion,
       [CompletionRelevance relevance = CompletionRelevance.DEFAULT, bool isDeprecated
       = false, bool isPotential = false]) {
-    var cs =
-        suggestions.firstWhere((cs) => cs.completion == completion, orElse: () {
+    var cs;
+    suggestions.forEach((s) {
+      if (s.completion == completion) {
+        if (cs == null) {
+          cs = s;
+        } else {
+          fail('expected exactly one $completion but found > 1');
+        }
+      }
+    });
+    if (cs == null) {
       var completions = suggestions.map((s) => s.completion).toList();
       fail('expected "$completion" but found\n $completions');
-    });
+    }
     expect(cs.kind, equals(kind));
     expect(cs.relevance, equals(relevance));
     expect(cs.selectionOffset, equals(completion.length));
     expect(cs.selectionLength, equals(0));
     expect(cs.isDeprecated, equals(isDeprecated));
     expect(cs.isPotential, equals(isPotential));
   }
 
   void assertSuggestClass(String className, [CompletionRelevance relevance =
       CompletionRelevance.DEFAULT]) {
@@ skipping 75 matching lines @@
   }
 
   @override
   void setUp() {
     super.setUp();
     index = createLocalMemoryIndex();
     searchEngine = new SearchEngineImpl(index);
     addResolvedUnit(MockSdk.LIB_CORE.path, MockSdk.LIB_CORE.content);
   }
 }