Update tests to check for as_api_object-specific things.

Good idea, but the errors were being generated by base R/weren't saying anything useful (they were the general "missing argument" messages). I've updated them to focus on the things as_api_object does specifically, to separate a failure of this function from all the places it's used within the package.

tests/testthat/test-as.R

@@ -1,10 +1,28 @@
-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()))
+test_that("as_api_object() fails informatively with bad x", {
+  simple_class <- S7::new_class(
+    "range",
+    properties = list(
+      start = S7::class_numeric,
+      end = S7::class_numeric
+    )
+  )
+  expect_no_error(as_api_object(NULL, simple_class))
+  expect_error(
+    as_api_object(1, simple_class),
+    class = "rapid_error_unknown_coercion"
+  )
+})
 
-  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))
+test_that("as_api_object() warns about unexpected fields", {
+  simple_class <- S7::new_class(
+    "range",
+    properties = list(
+      start = S7::class_numeric,
+      end = S7::class_numeric
+    )
+  )
+  expect_warning(
+    {as_api_object(list(start = 1, end = 2, a = 1), simple_class)},
+    class = "rapid_warning_extra_names"
+  )
 })