Disable private seed in testmode

Fixes #3816

Enables deterministic tests when the `shiny.testmode` option
is TRUE or when an app is run with `test.mode = TRUE`.

R/utils.R

@@ -52,6 +52,11 @@ repeatable <- function(rngfunc, seed = stats::runif(1, 0, .Machine$integer.max))
 # Evaluate an expression using Shiny's own private stream of
 # randomness (not affected by set.seed).
 withPrivateSeed <- function(expr) {
+  # Don't use the private seed in testmode for deterministic tests
+  if (isTRUE(getOption("shiny.testmode", getShinyOption("testmode")))) {
+    return(expr)
+  }
+
   # Save the old seed if present.
   if (exists(".Random.seed", envir = .GlobalEnv, inherits = FALSE)) {
     hasOrigSeed <- TRUE

tests/testthat/test-utils.R

@@ -50,6 +50,18 @@ test_that("Setting the private seed explicitly results in identical values", {
   expect_identical(id7, id8)
 })
 
+test_that("Private seed is disabled in testmode", {
+  oldopts <- options(shiny.testmode = TRUE)
+  on.exit(options(oldopts), add = TRUE)
+
+  set.seed(0)
+  id1 <- createUniqueId(4)
+  set.seed(0)
+  id2 <- createUniqueId(4)
+
+  expect_identical(id1, id2)
+})
+
 test_that("Private and 'public' random streams are independent and work the same", {
   set.seed(0)
   public <- c(runif(1), runif(1), runif(1))