add types for custom vitest assertions

Author: dyc3

server/tests/unit/api/room.spec.ts

@@ -142,7 +142,6 @@ describe("Room API", () => {
 				.expect("Content-Type", /json/)
 				.expect(404);
 			expect(resp.body.success).toEqual(false);
-			// @ts-expect-error I can't get typescript to acknowledge the custom matchers.
 			expect(resp.body.error).toBeRoomNotFound();
 		});
 	});

server/tests/unit/vitest.d.ts

@@ -0,0 +1,11 @@
+import type { Assertion, AsymmetricMatchersContaining } from "vitest";
+
+interface OttMatchers<R = unknown> {
+	toBeRoomNotFound: () => R;
+	toBeUnknownError: () => R;
+}
+
+declare module "vitest" {
+	interface Assertion<T = any> extends OttMatchers<T> {}
+	interface AsymmetricMatchersContaining extends OttMatchers {}
+}