BufferedReader ready() method always true

I am trying to test a method in a class which uses a BufferedReader intance:

public class ClassTotest {
  private BufferedReader reader;

public boolean methodToTest(){
  while (reader.ready()){
     reader.readLine();
  }
  more code
}
}

In my test class I initialized the reader instance using reflection:

class MyTest{
 @Test
 public void test(){
   ClassTotest testClass = new ClassTotest();
   Field reader = ClassTotest.class
            .getDeclaredField("reader");
   reader.setAccessible(true);
   StringReader stringReader = new StringReader("testString");
   BufferedReader readerToSet = new BufferedReader(stringReader);
   reader.set(testClass, readerToSet);
   testClass.methodToTest();
 }

It goes into the method and I can see that the reader object is initialized, but it always returns true when asked if ready(). So it goes into a infinite loop.

How can I initialize the reader to avoid this infinite loop?