From d4f10cf7efb95c78e0c57c213b55c92d4afc317c Mon Sep 17 00:00:00 2001
From: Rich FitzJohn <r.fitzjohn@imperial.ac.uk>
Date: Fri, 30 Aug 2024 14:52:41 +0100
Subject: [PATCH] Add assertion

---
 R/standalone-utils-assert.R       | 10 ++++++++++
 tests/testthat/test-util-assert.R |  8 ++++++++
 2 files changed, 18 insertions(+)

diff --git a/R/standalone-utils-assert.R b/R/standalone-utils-assert.R
index 8a7e382..a70e789 100644
--- a/R/standalone-utils-assert.R
+++ b/R/standalone-utils-assert.R
@@ -141,6 +141,16 @@ assert_is <- function(x, what, name = deparse(substitute(x)), arg = name,
 }
 
 
+assert_list <- function(x, name = deparse(substitute(x)), arg = name,
+                        call = parent.frame()) {
+  if (!is.list(x)) {
+    cli::cli_abort("Expected '{name}' to be a list",
+                   arg = arg, call = call)
+  }
+  invisible(x)
+}
+
+
 assert_named <- function(x, unique = FALSE, name = deparse(substitute(x)),
                          arg = name, call = parent.frame()) {
   nms <- names(x)
diff --git a/tests/testthat/test-util-assert.R b/tests/testthat/test-util-assert.R
index 2dfe149..5a7ae92 100644
--- a/tests/testthat/test-util-assert.R
+++ b/tests/testthat/test-util-assert.R
@@ -103,3 +103,11 @@ test_that("assert_scalar_logical", {
   expect_no_error(assert_scalar_logical(TRUE))
   expect_error(assert_scalar_logical(1), "to be logical")
 })
+
+
+test_that("assert_list", {
+  expect_silent(assert_list(list()))
+  expect_silent(assert_list(list(a = 1)))
+  x <- c(a = 1)
+  expect_error(assert_list(x), "Expected 'x' to be a list")
+})