Update SOURCE_KIND when a missing source file appears

pkg/analyzer/test/src/context/context_test.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 analyzer.test.src.context.context_test;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2530 matching lines @@
     _performPendingAnalysisTasks();
     expect(context.getErrors(sourceA).errors, hasLength(0));
     expect(context.getErrors(sourceB).errors, hasLength(0));
     // The a.dart's unit and element are the same.
     {
       LibrarySpecificUnit target = new LibrarySpecificUnit(sourceA, sourceA);
       expect(analysisCache.getValue(target, RESOLVED_UNIT), same(unitA));
       expect(unitA.element, same(unitElementA));
       expect(unitElementA.library, same(libraryElementA));
     }
-    // Update a.dart, rename A to A2, invalidates b.dart, so
+    // Add method to a.dart. This invalidates b.dart, so
     // we know that the previous update did not damage dependencies.
     context.setContents(
         sourceA,
         r'''
 library lib_a;
 class A {
   A();
   m() {}
 }
 class B {
@@ skipping 191 matching lines @@
 ''');
     _assertInvalid(sourceA, LIBRARY_ERRORS_READY);
     _assertInvalid(sourceB, LIBRARY_ERRORS_READY);
     _assertInvalid(sourceC, LIBRARY_ERRORS_READY);
     // No errors, "A.m" exists.
     _performPendingAnalysisTasks();
     expect(context.getErrors(sourceC).errors, hasLength(0));
   }
 
   void _assertInvalid(AnalysisTarget target, ResultDescriptor descriptor) {
-    CacheState state = analysisCache.getState(target, descriptor);
-    expect(state, CacheState.INVALID);
+    CacheState actual = analysisCache.getState(target, descriptor);
+    if (actual != CacheState.INVALID) {
+      fail("cache state of $target $descriptor: wanted INVALID, got: $actual");
+    }
   }
 
   void _assertValid(AnalysisTarget target, ResultDescriptor descriptor) {
     CacheState state = analysisCache.getState(target, descriptor);
     expect(state, CacheState.VALID);
   }
 
   void _performPendingAnalysisTasks([int maxTasks = 512]) {
     for (int i = 0; context.performAnalysisTask().hasMoreWork; i++) {
       if (i > maxTasks) {
@@ skipping 103 matching lines @@
    * Initialize the visitor.
    */
   _ElementGatherer();
 
   @override
   void visitElement(Element element) {
     elements[element] = element;
     super.visitElement(element);
   }
 }