Unit testing a class dependent on System clock

ClassUnderTest.java

/*
 * This is a mockup of JLine2 library structure. I am working on a feature that provides timestamp
 * and wanted to test it and hence this gist. The question that I asking via this gist is that how
 * should I test MemoryHistory?  
 */


/**
 * Represents the history of commands a user has given to a system via any interface such as
 * Command Line
 */
public interface History {
    void add(String command);
}

/**
 * A in memory history that keeps the history in memory and does not preserve history
 */
class MemoryHistory implements History {
    private List<String> commands;
    private List<long> timestamps;

    @Override
    public add(String command) {
      commands.add(command);
      timestamps.add(System.currentTimeMillis()); // here is the dependency on system time
    }    
}


/**
 * Possible approach 1: Create a default constructor that takes a TimeSource interface as an
 * argument and use that as a source of timestamp
 */
interface TimeSource {
    long currentTimeMillis();
}

/*
 * Adding a constructor with package visibility to accept a parameter, TimeSource 
 */
class MemoryHistory implements History {
   MemoryHistory(TimeSource timesource) {
      // now I can unit test the code with predictable values
   }
}

/*
 * So the question is should I create an extra indirection for unit testing something dependent
 * on time? Does that spoil the design? I viewed the "Is TDD Dead?" series and have started to
 * think a bit more on Test induced damage. So I was wondering whether this damages the design
 * or is there a better approach to do this?
 */