Add unit tests for copy/paste support

pkg/analysis_server/test/src/computer/imported_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/imported_elements_computer.dart';
+import 'package:analyzer/dart/analysis/results.dart';
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import '../../abstract_context.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ImportElementsComputerTest);
+  });
+}
+
+@reflectiveTest
+class ImportElementsComputerTest extends AbstractContextTest {
+  String sourcePath;
+
+  setUp() {
+    super.setUp();
+    sourcePath = provider.convertPath('/p/lib/source.dart');
+  }
+
+  test_none() async {
+    String selection = 'x + y + 1';
+    String content = """
+plusThree(int x) {
+  int y = 2;
+  print($selection);
+}
+""";
+    List<ImportedElements> elements = await _computeElements(
+        content, content.indexOf(selection), selection.length);
+    expect(elements, hasLength(0));
+  }
+
+  Future<List<ImportedElements>> _computeElements(
+      String sourceContent, int offset, int length) async {
+    provider.newFile(sourcePath, sourceContent);
+    ResolveResult result = await driver.getResult(sourcePath);
+    ImportedElementsComputer computer =
+        new ImportedElementsComputer(result.unit, offset, length);
+    return computer.compute();
+  }
+}