diff --git a/tests/testthat/test-as.R b/tests/testthat/test-as.R
new file mode 100644
index 0000000..7948933
--- /dev/null
+++ b/tests/testthat/test-as.R
@@ -0,0 +1,10 @@
+test_that("as_api_object() checks argument `x` ", {
+  expect_error(as_api_object())
+  expect_error(as_api_object(NULL))
+  expect_error(as_api_object(list()))
+
+  L <- list(a = "one") # named list
+  M <- c(a = "one") # named character vector
+  expect_error(as_api_object(L))
+  expect_error(as_api_object(M))
+})