Shiny Reactive Context in testthat test

Question

I am trying to execute code that requires a reactive context (but not the whole server)

library(shiny)
library(testthat)

test_that("test ", {
  withReactiveDomain(MockShinySession$new(), {
    v <- reactiveVal()
    v("abc")
    val <- v()
    expect_equal("abc", val)
  })
})

Then I get the following error:

Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)
Backtrace:
 1. shiny::withReactiveDomain(...) test_integration.R:45:2
 5. shiny:::v() test_integration.R:48:4
 6. rv$get()
 7. private$dependents$register()
 8. shiny:::getCurrentContext()
 9. .getReactiveEnvironment()$currentContext()

What am I missing? If I execute the inner block in an R session I get the same error.

Answer 1

A solution with the unexported function flushReact :

library(shiny)

x <- reactiveVal()
observe({
  message(x())
})
x("abc")

capture.output(shiny:::flushReact(), type = "message")
# [1] "abc"

Answer 2

Solution by @anddt

library(shiny)
library(testthat)

test_that("test ", {
  withReactiveDomain(MockShinySession$new(), {
    v <- reactiveVal()
    v("abc")
    val <- isolate(v())
    expect_equal("abc", val)
  })
})