Determining the largest sum of contiguous integers in a list
Unit testing

As it currently stands, testing your class means having to feed it a filesystem-based input (even if it's using something in-memory like Jimfs). You should consider implementing your application logic such that the input is the form of Stream&lt;String&gt;, so that the source of that stream is independent of the processing here.

String splitting as Stream&lt;String&gt;

Array.asList(string.split(",")).stream()


This can be better represented using Pattern.splitAsStream(CharSequence)

// consider making Pattern.compile(",") a static Pattern field too
Pattern.compile(",").splitAsStream(string)