improve import uri completions - fixes #24000

pkg/analysis_server/test/abstract_context.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 testing.abstract_context;
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_resolver.dart';
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 23 matching lines @@
 
 /**
  * A function to be called for every [Element].
  */
 typedef void _ElementVisitorFunction(Element element);
 
 class AbstractContextTest {
   static final DartSdk SDK = new MockSdk();
   static final UriResolver SDK_RESOLVER = new DartUriResolver(SDK);
 
-  MemoryResourceProvider provider = new MemoryResourceProvider();
+  MemoryResourceProvider provider;
   Map<String, List<Folder>> packageMap;
   UriResolver resourceResolver;
   AnalysisContext context;
 
   Source addPackageSource(String packageName, String filePath, String content) {
     packageMap[packageName] = [(provider.newFolder('/pubcache/$packageName'))];
     File file = provider.newFile('/pubcache/$packageName/$filePath', content);
     return file.createSource();
   }
 
@@ skipping 21 matching lines @@
 
   CompilationUnit resolveDartUnit(Source unitSource, Source librarySource) {
     return context.resolveCompilationUnit2(unitSource, librarySource);
   }
 
   CompilationUnit resolveLibraryUnit(Source source) {
     return context.resolveCompilationUnit2(source, source);
   }
 
   void setUp() {
+    setupResourceProvider();
     resourceResolver = new ResourceUriResolver(provider);
     packageMap = new Map<String, List<Folder>>();
     PackageMapUriResolver packageResolver =
         new PackageMapUriResolver(provider, packageMap);
     context = AnalysisEngine.instance.createAnalysisContext();
     context.sourceFactory =
         new SourceFactory([SDK_RESOLVER, packageResolver, resourceResolver]);
   }
 
+  void setupResourceProvider() {
+    provider = new MemoryResourceProvider();
+  }
+
   void tearDown() {
     context = null;
     provider = null;
   }
 }
 
 /**
  * Wraps the given [_ElementVisitorFunction] into an instance of
  * [engine.GeneralizingElementVisitor].
  */
 class _ElementVisitorFunctionWrapper extends GeneralizingElementVisitor {
   final _ElementVisitorFunction function;
   _ElementVisitorFunctionWrapper(this.function);
   visitElement(Element element) {
     function(element);
     super.visitElement(element);
   }
 }