Summary  
This chapter covers using variables to perform clear, concise, and efficient calculations.

General domain of usage  
Financial calculations.

library(testthat)
source(testthat::test_path("helper-run_user_code.R"), local = TRUE)

candidates <- c(
  testthat::test_path("..", "..", "user_code.R"),
  testthat::test_path("user_code.R")
)

candidates_norm <- vapply(
  candidates,
  function(p) tryCatch(normalizePath(p, winslash = "/", mustWork = FALSE), error = function(e) NA_character_),
  character(1)
)

exists_flags <- file.exists(candidates_norm)
if (!any(exists_flags)) {
  stop(
    sprintf(
      "user_code.R not found.\nChecked paths:\n  - %s\nWorking dir: %s",
      paste(candidates, collapse = "\n  - "),
      getwd()
    )
  )
}

user_file <- candidates_norm[which(exists_flags)[1]]

res <- run_user_code(
  file       = user_file,
  capture    = c("initial_money", "interest_rate", "n_years", "revenue"),
  echo       = FALSE,
  print.eval = TRUE
)

# 1) Проверка формулы revenue
{
  r  <- res$values$revenue
  rt <- res$values$initial_money * (1 + res$values$interest_rate / 100)^res$values$n_years

  ok <- !is.null(r) && isTRUE(all.equal(as.numeric(r), as.numeric(rt), tolerance = 1e-10))

  dynamic_test(
    ok,
    "Variable 'revenue' equals initial_money * (1 + interest_rate/100)^n_years",
    sprintf("Expected revenue = %.3f. Got: %s", rt, paste(utils::capture.output(dput(r)), collapse = " "))
  )
}

# 2) Проверка вывода (сравниваем 3 знака после запятой)
{
  rt <- res$values$initial_money * (1 + res$values$interest_rate / 100)^res$values$n_years
  expected_str <- sprintf("Accrued amount: %.3f", rt)

  out <- trimws(paste(res$logs, collapse = " "))
  ok  <- grepl(expected_str, out, fixed = TRUE)

  dynamic_test(
    ok,
    sprintf("Console output contains '%s'", expected_str),
    sprintf("Expected console output to include '%s'. Actual: %s", expected_str, out)
  )
}


test_hidden.R

run_user_code <- function(
  file = "user_code.R",
  capture = character(0),
  inject = list(),
  echo = FALSE,
  print.eval = TRUE
) {
  stopifnot(file.exists(file))

  env <- new.env(parent = baseenv())
  if (length(inject)) list2env(inject, envir = env)

  logs <- utils::capture.output(
    base::source(file, local = env, echo = echo, print.eval = print.eval)
  )

  values <- setNames(vector("list", length(capture)), capture)
  for (nm in capture) {
    if (exists(nm, envir = env, inherits = FALSE)) {
      values[[nm]] <- get(nm, envir = env, inherits = FALSE)
    } else {
      values[[nm]] <- NULL
    }
  }

  list(values = values, logs = logs, env = env)
}

# Один test_that с динамическим названием
dynamic_test <- function(condition, success, failure) {
  testthat::test_that(
    if (isTRUE(condition)) success else failure,
    {
      if (isTRUE(condition)) {
        testthat::expect_true(TRUE)
      } else {
        testthat::fail(failure)
      }
    }
  )
}


helper-run_user_code.R

A focused introduction to R for absolute beginners, covering the essentials: R syntax, variables, basic data types, and simple data operations. This course provides the foundational knowledge needed to start working with R confidently.

Challenge: Revenue Calculation

Solution

Challenge: Revenue Calculation

Solution