Use single unit/node/element.

pkg/analysis_server/test/domain_analysis_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 test.domain.analysis;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 98 matching lines @@
           String fileA = '/project/aaa/a.dart';
           String fileB = '/project/bbb/b.dart';
           resourceProvider.newFile(fileA, '// a');
           resourceProvider.newFile(fileB, '// b');
           var response = testSetAnalysisRoots(['/project'], ['/project/bbb']);
           var serverRef = server;
           expect(response, isResponseSuccess('0'));
           // unit "a" is resolved eventually
           // unit "b" is not resolved
           return server.onAnalysisComplete.then((_) {
-            expect(serverRef.getResolvedCompilationUnits(fileA), hasLength(1));
-            expect(serverRef.getResolvedCompilationUnits(fileB), isEmpty);
+            expect(serverRef.getResolvedCompilationUnit(fileA), isNotNull);
+            expect(serverRef.getResolvedCompilationUnit(fileB), isNull);
           });
         });
 
         test('not absolute', () async {
           var response = testSetAnalysisRoots([], ['foo/bar']);
           expect(
               response,
               isResponseFailure(
                   '0', RequestErrorCode.INVALID_FILE_PATH_FORMAT));
         });
@@ skipping 10 matching lines @@
       group('included', () {
         test('new folder', () {
           String file = '/project/bin/test.dart';
           resourceProvider.newFile('/project/pubspec.yaml', 'name: project');
           resourceProvider.newFile(file, 'main() {}');
           var response = testSetAnalysisRoots(['/project'], []);
           var serverRef = server;
           expect(response, isResponseSuccess('0'));
           // verify that unit is resolved eventually
           return server.onAnalysisComplete.then((_) {
-            var units = serverRef.getResolvedCompilationUnits(file);
-            expect(units, hasLength(1));
+            var unit = serverRef.getResolvedCompilationUnit(file);
+            expect(unit, isNotNull);
           });
         });
 
         test('nonexistent folder', () async {
           String fileB = '/project_b/b.dart';
           resourceProvider.newFile(fileB, '// b');
           var response = testSetAnalysisRoots(['/project_a', '/project_b'], []);
           var serverRef = server;
           expect(response, isResponseSuccess('0'));
           // Non-existence of /project_a should not prevent files in /project_b
           // from being analyzed.
           await server.onAnalysisComplete;
-          expect(serverRef.getResolvedCompilationUnits(fileB), hasLength(1));
+          expect(serverRef.getResolvedCompilationUnit(fileB), isNotNull);
         });
 
         test('not absolute', () async {
           var response = testSetAnalysisRoots(['foo/bar'], []);
           expect(
               response,
               isResponseFailure(
                   '0', RequestErrorCode.INVALID_FILE_PATH_FORMAT));
         });
 
@@ skipping 599 matching lines @@
   test_beforeAnalysis() async {
     addTestFile('int V = 42;');
     createProject();
     // subscribe
     addAnalysisSubscription(AnalysisService.HIGHLIGHTS, testFile);
     // wait for analysis
     await waitForTasksFinished();
     expect(filesHighlights[testFile], isNotEmpty);
   }
 }