Add code to locate a plugin within a package

pkg/analysis_server/test/src/plugin/plugin_locator_test.dart

Index: pkg/analysis_server/test/src/plugin/plugin_locator_test.dart
diff --git a/pkg/analysis_server/test/src/plugin/plugin_locator_test.dart b/pkg/analysis_server/test/src/plugin/plugin_locator_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..956987cc473e14adb4474ad04a5a34a2e84f4944
--- /dev/null
+++ b/pkg/analysis_server/test/src/plugin/plugin_locator_test.dart
@@ -0,0 +1,90 @@
+// 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 'package:analysis_server/src/plugin/plugin_locator.dart';
+import 'package:analyzer/file_system/memory_file_system.dart';
+import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(PluginLocatorTest);
+  });
+}
+
+@reflectiveTest
+class PluginLocatorTest {
+  MemoryResourceProvider resourceProvider;
+  String packageRoot;
+  String pubspecPath;
+  String defaultDirPath;
+  PluginLocator locator;
+
+  void setUp() {
+    resourceProvider = new MemoryResourceProvider();
+    packageRoot = resourceProvider.convertPath('/package');
+    resourceProvider.newFolder(packageRoot);
+    locator = new PluginLocator(resourceProvider);
+  }
+
+  void test_findPlugin_inPubspec_defaultDir() {
+    String dirPath = _createPubspecWithKey();
+    _createDefaultDir();
+    expect(locator.findPlugin(packageRoot), dirPath);
+  }
+
+  void test_findPlugin_inPubspec_noDefaultDir() {
+    String dirPath = _createPubspecWithKey();
+    expect(locator.findPlugin(packageRoot), dirPath);
+  }
+
+  void test_findPlugin_noPubspec_defaultDir() {
+    _createDefaultDir();
+    expect(locator.findPlugin(packageRoot), defaultDirPath);
+  }
+
+  void test_findPlugin_noPubspec_noDefaultDir() {
+    expect(locator.findPlugin(packageRoot), isNull);
+  }
+
+  void test_findPlugin_notInPubspec_defaultDir() {
+    _createPubspecWithoutKey();
+    _createDefaultDir();
+    expect(locator.findPlugin(packageRoot), defaultDirPath);
+  }
+
+  void test_findPlugin_notInPubspec_noDefaultDir() {
+    _createPubspecWithoutKey();
+    expect(locator.findPlugin(packageRoot), isNull);
+  }
+
+  void _createDefaultDir() {
+    defaultDirPath = resourceProvider.pathContext.join(packageRoot,
+        PluginLocator.toolsFolderName, PluginLocator.defaultPluginFolderName);
+    resourceProvider.newFolder(defaultDirPath);
+  }
+
+  void _createPubspec(String content) {
+    pubspecPath = resourceProvider.pathContext
+        .join(packageRoot, PluginLocator.pubspecFileName);
+    resourceProvider.newFile(pubspecPath, content);
+  }
+
+  String _createPubspecWithKey() {
+    String nonDefaultPath =
+        resourceProvider.pathContext.join(packageRoot, 'pluginDir');
+    _createPubspec('''
+name: test_project
+${PluginLocator.analysisPluginKey}: $nonDefaultPath
+''');
+    resourceProvider.newFolder(nonDefaultPath);
+    return nonDefaultPath;
+  }
+
+  void _createPubspecWithoutKey() {
+    _createPubspec('''
+name: test_project
+''');
+  }
+}