Don't mock random ids in test

Summary: This test started failing because new code paths called randomId() more often than expected, since we mock randomId like 5 times. This is super fragile. The better way is to just find whatever ID the request was made with and have the tests make sure the matching ID is sent, which is what we're actually testing.

Reviewed By: quark-zju

Differential Revision: D75693282

fbshipit-source-id: affb8920d32e5b795ba8137e3557ca9e915e25e4

Author: evangrayk

addons/isl/src/testUtils.tsx

@@ -30,10 +30,10 @@ export function simulateMessageFromServer(message: ServerToClientMessage): void
 }
 
 /** Filter out binary messages, and filter by wanted type. */
-function filterMessages(wantedType?: string) {
+function filterMessages<K extends string>(wantedType?: K) {
   let messages = testMessageBus.sent
     .filter((msg: unknown): msg is string => !(msg instanceof ArrayBuffer))
-    .map(deserializeFromString) as Array<Partial<ClientToServerMessage>>;
+    .map(deserializeFromString) as Array<ClientToServerMessage>;
   if (wantedType != null) {
     messages = messages.filter(msg => msg.type == null || msg.type === wantedType);
   }
@@ -44,6 +44,13 @@ export function expectMessageSentToServer(message: Partial<ClientToServerMessage
   expect(filterMessages(message.type)).toContainEqual(message);
 }
 
+export function getLastMessageOfTypeSentToServer<K extends string>(
+  wantedType: K,
+): (ClientToServerMessage & {type: K}) | undefined {
+  const values = filterMessages(wantedType) as Array<ClientToServerMessage & {type: K}>;
+  return values[values.length - 1];
+}
+
 export function expectMessageNOTSentToServer(message: Partial<ClientToServerMessage>): void {
   expect(filterMessages(message.type)).not.toContainEqual(message);
 }