chore: add assertIsPrice() test (denoland#579)

utils/stripe.ts

@@ -21,6 +21,18 @@ export const stripe = new Stripe(STRIPE_SECRET_KEY!, {
   httpClient: Stripe.createFetchHttpClient(),
 });
 
+/**
+ * Asserts that the value is strictly a {@linkcode Stripe.Price} object.
+ *
+ * @example
+ * ```ts
+ * import { assertIsPrice } from "@/utils/stripe.ts";
+ *
+ * assertIsPrice(undefined); // Throws AssertionError
+ * assertIsPrice(null); // Throws AssertionError
+ * assertIsPrice("not a price"); // Throws AssertionError
+ * ```
+ */
 export function assertIsPrice(value: unknown): asserts value is Stripe.Price {
   if (value === undefined || value === null || typeof value === "string") {
     throw new AssertionError(

utils/stripe_test.ts

@@ -0,0 +1,11 @@
+// Copyright 2023 the Deno authors. All rights reserved. MIT license.
+import { AssertionError, assertThrows } from "std/assert/mod.ts";
+import { assertIsPrice } from "./stripe.ts";
+
+Deno.test("[stripe] assertIsPrice()", () => {
+  const message =
+    "Default price must be of type `Stripe.Price`. Please run the `deno task init:stripe` as the README instructs.";
+  assertThrows(() => assertIsPrice(undefined), AssertionError, message);
+  assertThrows(() => assertIsPrice(null), AssertionError, message);
+  assertThrows(() => assertIsPrice("not a price"), AssertionError, message);
+});