Usage
testMatrixvariate(
  object,
  errormsg = paste(object$short_name, "is not matrixvariate")
)checkMatrixvariate(
  object,
  errormsg = paste(object$short_name, "is not matrixvariate")
)
assertMatrixvariate(
  object,
  errormsg = paste(object$short_name, "is not matrixvariate")
)