New()

Select("A")
SetGlyphName("A")
SetWidth(100)

Select("B")
SetGlyphName("B")
SetWidth(100)

Select("C")
SetGlyphName("C")
SetWidth(100)

Select("D")
SetGlyphName("D")
SetWidth(100)

MergeFeature($1)

lookups = GetLookups("GSUB")
if (SizeOf(lookups) != 2)
  Error("There should be two lookups")
endif

i = 0
while (i < SizeOf(lookups))
  subtables = GetLookupSubtables(lookups[i])
  if (SizeOf(subtables) != 1)
    Print("Lookup: ", lookups[i])
    Error("There should be one subtable")
  endif
  if (i == 1)
    Select("A")
    sub = GetPosSub(subtables[0])
    if (SizeOf(sub) != 1)
      Error("Incorrect number of substitutions")
    endif
    if (SizeOf(sub[0]) != 4 || sub[0][1] != "MultSubs" || sub[0][2] != "C" || sub[0][3] != "D")
      Error("Incorrect substitution")
    endif
  endif
  i++
endloop

Close()