Unit Testing Philosophy

I have a recipe method that I am trying to write using TDD. He mainly addresses various methods and sometimes makes decisions based on the results of these methods:

  public void HandleNewData(Data data)
  {
     var existingDataStore = dataProvider.Find(data.ID);
     if (data == null)
        return;

     UpdateDataStore(existingDataStore, data, CurrentDateTime);

     NotifyReceivedData(data);

     if (!dataValidator.Validate(data))
        return;

     //... more operations similar to above
  }

My knee-jerk reaction would be to start writing test cases when I verify that HandleNewData calls the methods described above, passing the expected arguments and returned when the method call fails. But for me it seems like it is a huge investment on time to encode such a test with virtually no actual benefit.

So what is the real benefit of writing such a test? Or is it really not worth the bother?

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