Fix insertion of imports when there are no existing directives (issue 30430)

pkg/analysis_server/test/src/computer/import_elements_computer_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/computer/import_elements_computer.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
@@ skipping 40 matching lines @@
     provider.newFile(path, content);
     AnalysisResult result = await driver.getResult(path);
     computer = new ImportElementsComputer(provider, result);
   }
 
   void setUp() {
     super.setUp();
     path = provider.convertPath('/test.dart');
   }
 
+  test_createEdits_addImport_noDirectives() async {

[scheglov, 2017/08/14 18:37:51]

Maybe also worth to add a test with parts.

[Brian Wilkerson, 2017/08/14 19:59:20]

Absolutely. In fact, I think you found a bug. But I think the bug is outside
this class, so this isn't the right place for the test. Hence, I'll add it in a
separate CL.

+    await createBuilder('''
+main() {
+  // paste here
+}
+''');
+    await computeChanges(<ImportedElements>[
+      new ImportedElements('/lib/math/math.dart', '', <String>['Random'])
+    ]);
+    assertChanges('''
+import 'dart:math';
+
+main() {
+  // paste here
+}
+''');
+  }
+
   test_createEdits_addImport_noPrefix() async {
     Source fooSource = addPackageSource('pkg', 'foo.dart', '');
     await createBuilder('''
 import 'package:pkg/foo.dart' as foo;
 ''');
     await computeChanges(<ImportedElements>[
       new ImportedElements(fooSource.fullName, '', <String>['A'])
     ]);
     assertChanges('''
 import 'package:pkg/foo.dart' as foo;
@@ skipping 245 matching lines @@
 import 'package:pkg/foo.dart' hide A, B;
 ''');
     await computeChanges(<ImportedElements>[
       new ImportedElements(fooSource.fullName, '', <String>['A', 'B'])
     ]);
     assertChanges('''
 import 'package:pkg/foo.dart';
 ''');
   }
 }