Implement mock_output_sequence() (#2061)

Similar to {mockery}'s multiple return values

DESCRIPTION

@@ -56,4 +56,4 @@ Config/testthat/parallel: true
 Config/testthat/start-first: watcher, parallel*
 Encoding: UTF-8
 Roxygen: list(markdown = TRUE, r6 = FALSE)
-RoxygenNote: 7.3.2
+RoxygenNote: 7.3.2.9000

NAMESPACE

@@ -164,6 +164,7 @@ export(local_test_context)
 export(local_test_directory)
 export(make_expectation)
 export(matches)
+export(mock_output_sequence)
 export(new_expectation)
 export(not)
 export(prints_text)

R/mock2-helpers.R

@@ -0,0 +1,49 @@
+#' Mock a sequence of output from a function
+#'
+#' Specify multiple return values for mocking
+#'
+#' @param ... <[`dynamic-dots`][rlang::dyn-dots]> Values to return in sequence.
+#' @param recycle whether to recycle. If `TRUE`, once all values have been returned,
+#' they will be returned again in sequence.
+#'
+#' @return A function that you can use within `local_mocked_bindings()` and
+#' `with_mocked_bindings()`
+#' @export
+#'
+#' @examples
+#' # inside local_mocked_bindings()
+#' \dontrun{
+#' local_mocked_bindings(readline = mock_output_sequence("3", "This is a note", "n"))
+#' }
+#' # for understanding
+#' mocked_sequence <- mock_output_sequence("3", "This is a note", "n")
+#' mocked_sequence()
+#' mocked_sequence()
+#' mocked_sequence()
+#' try(mocked_sequence())
+#' recycled_mocked_sequence <- mock_output_sequence(
+#'   "3", "This is a note", "n",
+#'   recycle = TRUE
+#' )
+#' recycled_mocked_sequence()
+#' recycled_mocked_sequence()
+#' recycled_mocked_sequence()
+#' recycled_mocked_sequence()
+#' @family mocking
+mock_output_sequence <- function(..., recycle = FALSE) {
+  values <- rlang::list2(...)
+  i <- 1
+  function(...) {
+    if (i > length(values) && !recycle) {
+      cli::cli_abort(c(
+        "Can't find value for {i}th iteration.",
+        i = "{.arg ...} has only {length(values)} values.",
+        i = "You can set {.arg recycle} to {.code TRUE}."
+      ))
+    }
+    index <- (i - 1) %% length(values) + 1
+    value <- rep_len(values, length.out = index)[[index]]
+    i <<- i + 1
+    value
+  }
+}

R/mock2.R

@@ -92,6 +92,17 @@
 #'   my_wrapper = function(...) "new_value"
 #' )
 #' ```
+#'
+#' ## Multiple return values / sequence of outputs
+#'
+#' To mock a function that returns different values in sequence,
+#' for instance an API call whose status would be 502 then 200,
+#' or an user intput to `readline()`, you can use [mock_output_sequence()]
+#'
+#' ```R
+#' local_mocked_bindings(readline = mock_output_sequence("3", "This is a note", "n"))
+#' ```
+#'
 #' @export
 #' @param ... Name-value pairs providing new values (typically functions) to
 #'   temporarily replace the named bindings.
@@ -103,6 +114,7 @@
 #'   under active development (i.e. loaded with [pkgload::load_all()]).
 #'   We don't recommend using this to mock functions in other packages,
 #'   as you should not modify namespaces that you don't own.
+#' @family mocking
 local_mocked_bindings <- function(..., .package = NULL, .env = caller_env()) {
   bindings <- list2(...)
   check_bindings(bindings)

_pkgdown.yml

@@ -72,6 +72,7 @@ reference:
 - title: Mocking
   contents:
   - with_mocked_bindings
+  - starts_with("mock_")
 
 - title: Expectation internals
   contents:

tests/testthat/_snaps/mock2-helpers.md

@@ -0,0 +1,10 @@
+# mock_output_sequence() works
+
+    Code
+      mocked_sequence()
+    Condition
+      Error in `mocked_sequence()`:
+      ! Can't find value for 4th iteration.
+      i `...` has only 3 values.
+      i You can set `recycle` to `TRUE`.
+

tests/testthat/test-mock2-helpers.R

@@ -0,0 +1,29 @@
+test_that("mock_output_sequence() works", {
+  mocked_sequence <- mock_output_sequence("3", "This is a note", "n")
+  expect_equal(mocked_sequence(), "3")
+  expect_equal(mocked_sequence(), "This is a note")
+  expect_equal(mocked_sequence(), "n")
+  expect_snapshot(mocked_sequence(), error = TRUE)
+})
+
+test_that("mock_output_sequence() works -- list", {
+  x <- list("3", "This is a note", "n")
+  mocked_sequence <- mock_output_sequence(!!!x)
+  expect_equal(mocked_sequence(), "3")
+  expect_equal(mocked_sequence(), "This is a note")
+  expect_equal(mocked_sequence(), "n")
+})
+
+test_that("mock_output_sequence()'s recycling works", {
+  mocked_sequence <- mock_output_sequence(
+    "3", "This is a note", "n",
+    recycle = TRUE
+  )
+  expect_equal(mocked_sequence(), "3")
+  expect_equal(mocked_sequence(), "This is a note")
+  expect_equal(mocked_sequence(), "n")
+  expect_equal(mocked_sequence(), "3")
+  expect_equal(mocked_sequence(), "This is a note")
+  expect_equal(mocked_sequence(), "n")
+})
+