class SimpleCov::Formatter::Base

def entry_point_filename

that has no single canonical entry point.
leaves the bare directory in place for any third-party formatter
gets appended to the directory in the status line. Default nil
(e.g. `index.html` for HTML, `coverage.json` for JSON), which
Subclasses override to name the report's entry-point file 
def entry_point_filename
  nil
end