improve completion test failure message by adding node info

pkg/analysis_server/test/services/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_server/src/protocol.dart' as protocol show Element, ElementKind;
+import 'package:analysis_server/src/protocol.dart' as protocol show Element,
+    ElementKind;
 import 'package:analysis_server/src/protocol.dart' hide Element;
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analysis_server/src/services/index/local_memory_index.dart';
 import 'package:analysis_server/src/services/search/search_engine_internal.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../abstract_context.dart';
 
 class AbstractCompletionTest extends AbstractContextTest {
   Index index;
   SearchEngineImpl searchEngine;
   DartCompletionComputer computer;
   String testFile = '/completionTest.dart';
   Source testSource;
+  CompilationUnit testUnit;
   int completionOffset;
+  AstNode completionNode;
   bool _computeFastCalled = false;
   DartCompletionRequest request;
 
   void addResolvedUnit(String file, String code) {
     Source source = addSource(file, code);
     CompilationUnit unit = resolveLibraryUnit(source);
     index.indexUnit(context, unit);
   }
 
   void addTestSource(String content) {
     expect(completionOffset, isNull, reason: 'Call addTestUnit exactly once');
     completionOffset = content.indexOf('^');
     expect(completionOffset, isNot(equals(-1)), reason: 'missing ^');
     int nextOffset = content.indexOf('^', completionOffset + 1);
     expect(nextOffset, equals(-1), reason: 'too many ^');
     content = content.substring(0, completionOffset) +
         content.substring(completionOffset + 1);
     testSource = addSource(testFile, content);
     request =
         new DartCompletionRequest(context, searchEngine, testSource, completionOffset);
   }
 
   void assertNotSuggested(String completion) {
     if (request.suggestions.any((cs) => cs.completion == completion)) {
-      fail('did not expect completion: $completion');
+      _failWithNodeInfo('did not expect completion: $completion');
     }
   }
 
   CompletionSuggestion assertSuggest(CompletionSuggestionKind kind,
       String completion, [CompletionRelevance relevance = CompletionRelevance.DEFAULT,
       bool isDeprecated = false, bool isPotential = false]) {
     CompletionSuggestion cs;
     request.suggestions.forEach((s) {
       if (s.completion == completion) {
         if (cs == null) {
           cs = s;
         } else {
-          List<CompletionSuggestion> matchSuggestions =
+          List<CompletionSuggestion> completions =
               request.suggestions.where((s) => s.completion == completion).toList();
-          fail(
-              'expected exactly one $completion but found > 1\n $matchSuggestions');
+          _failWithNodeInfo(
+              'expected exactly one $completion but found > 1\n$completions');
         }
       }
     });
     if (cs == null) {
       List<CompletionSuggestion> completions =
           request.suggestions.map((s) => s.completion).toList();
-      fail('expected "$completion" but found\n $completions');
+      _failWithNodeInfo('expected "$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));
     return cs;
   }
 
@@ skipping 127 matching lines @@
     expect(element.name, equals(name));
     //TODO (danrubel) return type level variable 'type' but not as 'returnType'
 //    expect(
 //        element.returnType,
 //        equals(returnType != null ? returnType : 'dynamic'));
     return cs;
   }
 
   bool computeFast() {
     _computeFastCalled = true;
-    CompilationUnit unit = context.parseCompilationUnit(testSource);
-    request.unit = unit;
-    request.node = new NodeLocator.con1(completionOffset).searchWithin(unit);
+    testUnit = context.parseCompilationUnit(testSource);
+    completionNode =
+        new NodeLocator.con1(completionOffset).searchWithin(testUnit);
+    request.unit = testUnit;
+    request.node = completionNode;
     return computer.computeFast(request);
   }
 
   Future<bool> computeFull([bool fullAnalysis = false]) {
     if (!_computeFastCalled) {
       expect(computeFast(), isFalse);
     }
 
     // Index SDK
     for (Source librarySource in context.librarySources) {
@@ skipping 39 matching lines @@
     }
     return computer.computeFull(request);
   }
 
   @override
   void setUp() {
     super.setUp();
     index = createLocalMemoryIndex();
     searchEngine = new SearchEngineImpl(index);
   }
+
+  void _failWithNodeInfo(String message) {
+    StringBuffer sb = new StringBuffer(message);
+    if (completionNode != null) {
+      sb.write('\n  in');
+      AstNode node = completionNode;
+      while (node != null) {
+        sb.write('\n    ${node.runtimeType}');
+        node = node.parent;
+      }
+    }
+    fail(sb.toString());
+  }
 }