Ensure that RESOLVED_UNITx ready once for every library.

pkg/analyzer/test/src/task/dart_test.dart

 // Copyright (c) 2015, 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.src.task.dart_test;
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 823 matching lines @@
 ''',
       '/part1.dart': '''
 part of lib;
 int get test => 0;
 ''',
       '/part2.dart': '''
 part of lib;
 void set test(_) {}
 '''
     });
-    CompilationUnitElement unitElement1 = partUnits[0].element;
-    CompilationUnitElement unitElement2 = partUnits[1].element;
+    CompilationUnitElement unitElement1 = partUnits
+        .singleWhere((u) => u.element.name.endsWith('part1.dart'))
+        .element;
+    CompilationUnitElement unitElement2 = partUnits
+        .singleWhere((u) => u.element.name.endsWith('part2.dart'))
+        .element;
     PropertyAccessorElement getter = unitElement1.accessors[0];
     PropertyAccessorElement setter = unitElement2.accessors[0];
     PropertyInducingElement variable = getter.variable;
     expect(getter.isGetter, isTrue);
     expect(setter.isSetter, isTrue);
     expect(variable, isNotNull);
     expect(setter.variable, same(variable));
     expect(unitElement1.topLevelVariables, [variable]);
     expect(unitElement2.topLevelVariables, [variable]);
   }
@@ skipping 3561 matching lines @@
   /**
    * Fill [errorListener] with [result] errors in the current [task].
    */
   void _fillErrorListener(ResultDescriptor<List<AnalysisError>> result) {
     List<AnalysisError> errors = task.outputs[result];
     expect(errors, isNotNull, reason: result.name);
     errorListener = new GatheringErrorListener();
     errorListener.addAll(errors);
   }
 }