I’ve found a workaround to the problem discussed here:

https://groups.google.com/forum/?fromgroups#!category-topic/stan-users/general/8ayvLs229Ow

The problem is that sometimes you want to reset the RNG for Stan functions called from R, but the seed value passed is only used the first time. The solution I’ve found is to create the model once, but call expose_stan_functions() each time I want to reset the RNG. A unit test file using testthat then looks something like this:

```
sm <- (code to compute stan_model object)
stan_fcts_from_model <- function(model) {
e <- new.env(parent=baseenv())
expose_stan_functions(model, e)
e
}
...
test_that("Something", {
...
fcts <- stan_fcts_from_model(sm) # RNG will be reset on next line
x1 <- fcts$some_stan_function_I_defined_rng(..., my_seed)
....
fcts <- stan_fcts_from_model(sm) # RNG will be reset on next line
x2 <- fcts$some_stan_function_I_defined_rng(..., my_seed)
...
}
```