library(survey)
data(api)
dclus2<-svydesign(id=~dnum+snum, weights=~pw, data=apiclus2)
rclus2<-as.svrepdesign(dclus2)
model<-svyglm(formula = api00 ~ ell + meals + mobility, design = rclus2)
svycontrast(model, c(ell=1,meals=0))
a<-svycontrast(model, c(0,1,0,0))

model2<-svyglm(formula = api00 ~ ell + meals + mobility, design = rclus2,return.replicates=TRUE)
svycontrast(model2, c(ell=1,meals=0))
a2<-svycontrast(model2, c(0,1,0,0))
stopifnot(!is.null(a2$replicates))