R Under development (unstable) (2023-11-03 r85470 ucrt) -- "Unsuffered Consequences"
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> if (lme4:::testLevel() > 1 || .Platform$OS.type!="windows") {
+     ## example posted by Stéphane Laurent
+     ## exercises bug where Nelder-Mead min objective function value was >0
+     set.seed(666)
+     sims <- function(I, J, sigmab0, sigmaw0){
+         Mu <- rnorm(I, mean=0, sd=sigmab0)
+         y <- c(sapply(Mu, function(mu) rnorm(J, mu, sigmaw0)))
+         data.frame(y=y, group=gl(I,J))
+     }
+ 
+     I <- 3  # number of groups
+     J <- 8  # number of repeats per group
+     sigmab0 <- 0.15  # between standard deviation
+     sigmaw0 <- 0.15  # within standard deviation
+ 
+     dat <- sims(I, J, sigmab0, sigmaw0)
+ 
+     library(lme4)
+     isOldTol <- environment(nloptwrap)$defaultControl$xtol_abs == 1e-6
+ 
+     fm3 <- lmer(y ~ (1|group), data=dat)
+     stopifnot(all.equal(unname(unlist(VarCorr(fm3))),
+                         switch(fm3@optinfo$optimizer,
+                                "Nelder_Mead" = 0.029662844,
+                                "bobyqa"      = 0.029662698,
+                                "nloptwrap"   =
+                                    if (isOldTol) 0.029679755 else 0.029662699,
+                                stop("need new case here: value is ",unname(unlist(VarCorr(fm3))))
+                                ),
+                         tolerance = 1e-7))
+ } ## skip on windows (for speed)
> 
> proc.time()
   user  system elapsed 
   1.23    0.10    1.28