\version "2.19.35"

m = { d''32 e'' d''2... }
test = \markup \bold \rotate #90 "TEST"

\score {
  <<
  \new StaffGroup \new Staff \m
  \new StaffGroup <<
    \new Staff \m
    \new Staff \m
  >>
  >>
  \layout {
    \context {
      \StaffGroup
      instrumentName = \test
      \override InstrumentName.self-alignment-X = 1
    }
  }
}