1 files changed, 43 insertions, 0 deletions
diff --git a/tests/unit/esnext_test.ts b/tests/unit/esnext_test.ts
new file mode 100644
index 000000000..6b2334f42
--- /dev/null
+++ b/tests/unit/esnext_test.ts
@@ -0,0 +1,43 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+import { assertEquals } from "./test_util.ts";
+
+// TODO(@kitsonk) remove when we are no longer patching TypeScript to have
+// these types available.
+
+Deno.test(function typeCheckingEsNextArrayString() {
+  const b = ["a", "b", "c", "d", "e", "f"];
+  assertEquals(b.findLast((val) => typeof val === "string"), "f");
+  assertEquals(b.findLastIndex((val) => typeof val === "string"), 5);
+});
+
+Deno.test(function intlListFormat() {
+  const formatter = new Intl.ListFormat("en", {
+    style: "long",
+    type: "conjunction",
+  });
+  assertEquals(
+    formatter.format(["red", "green", "blue"]),
+    "red, green, and blue",
+  );
+
+  const formatter2 = new Intl.ListFormat("en", {
+    style: "short",
+    type: "disjunction",
+  });
+  assertEquals(formatter2.formatToParts(["Rust", "golang"]), [
+    { type: "element", value: "Rust" },
+    { type: "literal", value: " or " },
+    { type: "element", value: "golang" },
+  ]);
+
+  // Works with iterables as well
+  assertEquals(
+    formatter.format(new Set(["red", "green", "blue"])),
+    "red, green, and blue",
+  );
+  assertEquals(formatter2.formatToParts(new Set(["Rust", "golang"])), [
+    { type: "element", value: "Rust" },
+    { type: "literal", value: " or " },
+    { type: "element", value: "golang" },
+  ]);
+});