if (.Platform$OS.type != "windows") {
    library(lme4)
    library(testthat)
    fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy)
    expect_equal(colnames(model.frame(fm1)),c("Reaction","Days","Subject"))
    expect_equal(colnames(model.frame(fm1,fixed.only=TRUE)),c("Reaction","Days"))
    expect_equal(formula(fm1),Reaction ~ Days + (Days | Subject))
    expect_equal(formula(fm1,fixed.only=TRUE),Reaction ~ Days)

    ## ugly example: model frame with compound elements
    fm2 <- lmer(log(Reaction) ~ splines::ns(Days,3) +
                    + I(1+Days^3) + (Days|Subject), sleepstudy)
    expect_equal(names(model.frame(fm2)),
                 c("log(Reaction)", "splines::ns(Days, 3)",
                   "I(1 + Days^3)", "Days", "Subject"))
    expect_equal(names(model.frame(fm2,fixed.only=TRUE)),
                 c("log(Reaction)", "splines::ns(Days, 3)",
                   "I(1 + Days^3)"))

} ## skip on windows (for speed)