If there is a changed file, hasFilesToAnalyze is true.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

 // Copyright (c) 2016, 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.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 980 matching lines @@
     expect(driver.hasFilesToAnalyze, isFalse);
 
     // Ask to analyze the file, so there is a file to analyze.
     Future<AnalysisResult> future = driver.getResult(testFile);
     expect(driver.hasFilesToAnalyze, isTrue);
 
     // Once analysis is done, there is nothing to analyze.
     await future;
     expect(driver.hasFilesToAnalyze, isFalse);
 
+    // Change a file, even if not added, it still might affect analysis.
+    driver.changeFile(_p('/not/added.dart'));
+    expect(driver.hasFilesToAnalyze, isTrue);
+    await _waitForIdle();
+    expect(driver.hasFilesToAnalyze, isFalse);
+
     // Request of referenced names is not analysis of a file.
     driver.getFilesReferencingName('X');
     expect(driver.hasFilesToAnalyze, isFalse);
   }
 
   test_knownFiles() async {
     var a = _p('/test/lib/a.dart');
     var b = _p('/test/lib/b.dart');
     var c = _p('/test/lib/c.dart');
 
@@ skipping 588 matching lines @@
   String _p(String path) => provider.convertPath(path);
 
   Future<Null> _waitForIdle() async {
     await idleStatusMonitor.signal;
   }
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }