Only units with 'part of' and no other directives are parts.

pkg/analyzer/test/src/task/dart_test.dart

 // Copyright (c) 2015, 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.src.task.dart_test;
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 2153 matching lines @@
     expect(outputs[EXPLICITLY_IMPORTED_LIBRARIES], hasLength(0));
     expect(outputs[EXPORTED_LIBRARIES], hasLength(0));
     _assertHasCore(outputs[IMPORTED_LIBRARIES], 1);
     expect(outputs[INCLUDED_PARTS], hasLength(0));
     expect(outputs[PARSE_ERRORS], hasLength(0));
     expect(outputs[PARSED_UNIT], isNotNull);
     expect(outputs[SOURCE_KIND], SourceKind.PART);
     expect(outputs[UNITS], hasLength(1));
   }
 
-  test_perform_computeSourceKind_noDirectives_hasContainingLibraries() {
-    // Parse "lib.dart" to let the context know that "test.dart" is a part.
+  test_perform_computeSourceKind_noDirectives_hasContainingLibrary() {
+    // Parse "lib.dart" to let the context know that "test.dart" is included.
     _computeResult(newSource('/lib.dart', r'''
 library lib;
 part 'test.dart';
 '''), PARSED_UNIT);
-    // So, know "test.dat" is parsed as a part.
-    _performParseTask('');
-    expect(outputs[SOURCE_KIND], SourceKind.PART);
-  }
-
-  test_perform_computeSourceKind_noDirectives_noContainingLibraries() {
+    // If there are no the "part of" directive, then it is not a part.
     _performParseTask('');
     expect(outputs[SOURCE_KIND], SourceKind.LIBRARY);
   }
+
+  test_perform_computeSourceKind_noDirectives_noContainingLibrary() {
+    _performParseTask('');
+    expect(outputs[SOURCE_KIND], SourceKind.LIBRARY);
+  }
 
   test_perform_doesNotExist() {
     _performParseTask(null);
     expect(outputs, hasLength(8));
     expect(outputs[EXPLICITLY_IMPORTED_LIBRARIES], hasLength(0));
     expect(outputs[EXPORTED_LIBRARIES], hasLength(0));
     _assertHasCore(outputs[IMPORTED_LIBRARIES], 1);
     expect(outputs[INCLUDED_PARTS], hasLength(0));
     expect(outputs[PARSE_ERRORS], hasLength(0));
     expect(outputs[PARSED_UNIT], isNotNull);
@@ skipping 31 matching lines @@
     expect(outputs[EXPLICITLY_IMPORTED_LIBRARIES], hasLength(1));
     expect(outputs[EXPORTED_LIBRARIES], hasLength(1));
     _assertHasCore(outputs[IMPORTED_LIBRARIES], 2);
     expect(outputs[INCLUDED_PARTS], hasLength(1));
     expect(outputs[PARSE_ERRORS], hasLength(1));
     expect(outputs[PARSED_UNIT], isNotNull);
     expect(outputs[SOURCE_KIND], SourceKind.LIBRARY);
     expect(outputs[UNITS], hasLength(2));
   }
 
+  test_perform_part() {
+    _performParseTask(r'''
+part of lib;
+class B {}''');
+    expect(outputs, hasLength(8));
+    expect(outputs[EXPLICITLY_IMPORTED_LIBRARIES], hasLength(0));
+    expect(outputs[EXPORTED_LIBRARIES], hasLength(0));
+    _assertHasCore(outputs[IMPORTED_LIBRARIES], 1);
+    expect(outputs[INCLUDED_PARTS], hasLength(0));
+    expect(outputs[PARSE_ERRORS], hasLength(0));
+    expect(outputs[PARSED_UNIT], isNotNull);
+    expect(outputs[SOURCE_KIND], SourceKind.PART);
+    expect(outputs[UNITS], hasLength(1));
+  }
+
   void _performParseTask(String content) {
     AnalysisTarget target = newSource('/test.dart', content);
     _computeResult(target, PARSED_UNIT);
     expect(task, new isInstanceOf<ParseDartTask>());
   }
 
   static void _assertHasCore(List<Source> sources, int lenght) {
     expect(sources, hasLength(lenght));
     expect(sources, contains(predicate((Source s) {
       return s.fullName.endsWith('core.dart');
@@ skipping 384 matching lines @@
   /**
    * Fill [errorListener] with [result] errors in the current [task].
    */
   void _fillErrorListener(ResultDescriptor<List<AnalysisError>> result) {
     List<AnalysisError> errors = task.outputs[result];
     expect(errors, isNotNull, reason: result.name);
     errorListener = new GatheringErrorListener();
     errorListener.addAll(errors);
   }
 }