test_that("all theta parameters are fixed", {

  one.compartment <- function() {
    ini({
      tka <- fixed(log(1.57))
      tcl <- fixed(log(2.72))
      tv <- fixed(log(31.5))
      eta.ka ~ 0.6
      add.sd <- 0.7
    })
    # and a model block with the error specification and model specification
    model({
      ka <- exp(tka + eta.ka)
      cl <- exp(tcl)
      v <- exp(tv)
      cp <- linCmt()
      cp ~ add(add.sd)
    })
  }

  f <- nlmixr2(
    one.compartment, data = theo_sd, est="saem", control = saemControl(print=0, nEm=10, nBurn=10, literalFix=FALSE))

  expect_true(inherits(f, "nlmixr2FitData"))

  m2 <- rxode2::rxFixPop(one.compartment)

  expect_error(m2$saemModelPred, NA)

  f <- nlmixr2(
    one.compartment, data = theo_sd, est="saem", control = saemControl(print=0, nEm=10, nBurn=10, literalFix=TRUE))

  expect_true(inherits(f, "nlmixr2FitData"))

})