\version "2.13.35"

\score {
  \new StaffGroup <<
    \new GrandStaff = "group I"\with { \consists "Instrument_name_engraver" } <<
      \set GrandStaff.instrumentName = "group 1"
      \set GrandStaff.shortInstrumentName = "g1"
      \new RhythmicStaff = "test I" {
        \set RhythmicStaff.instrumentName = "test 1"
        \set RhythmicStaff.shortInstrumentName = "t1"
        c4 c c c | \break c c c c
      }
      \new RhythmicStaff = "test II" {
        \set RhythmicStaff.instrumentName = "test 2"
        \set RhythmicStaff.shortInstrumentName = "t2"
        c4 c c c | \break c c c c
      }
    >>
    \new GrandStaff = "group II" \with { \consists "Instrument_name_engraver" } <<
      \set GrandStaff.instrumentName = "group 2"
      \set GrandStaff.shortInstrumentName = "g2"
      \new RhythmicStaff = "test III" {
        \set RhythmicStaff.instrumentName = "test 3"
        \set RhythmicStaff.shortInstrumentName = "t3"
        c4 c c c | \break c c c c
      }
      \new RhythmicStaff = "test IV" {
        \set RhythmicStaff.instrumentName = "test 4"
        \set RhythmicStaff.shortInstrumentName = "t4"
        c4 c c c | \break c c c c
      }
    >>
  >>
  \layout { }
}