test: remove duplicate event listeners and check known events

Author: dariakp

test/tools/unified-spec-runner/entities.ts

@@ -119,15 +119,16 @@ export class UnifiedMongoClient extends MongoClient {
       'configureFailPoint'
     ];
 
-    this.observedEvents = (description.observeEvents ?? [])
-      .map(e => UnifiedMongoClient.EVENT_NAME_LOOKUP[e])
-      .filter(e => !!e);
-    this.observedEvents = (description.observeEvents ?? [])
-      .map(e => UnifiedMongoClient.EVENT_NAME_LOOKUP[e])
-      .filter(e => !!e);
-    for (const eventName of this.observedEvents) {
-      this.on(eventName, this.pushEvent);
+    this.observedEvents = [];
+
+    for (const e of description.observeEvents ?? []) {
+      const eventToObserve = UnifiedMongoClient.EVENT_NAME_LOOKUP[e];
+      if (!eventToObserve) {
+        throw new Error(`Unknown expected event: ${e}`);
+      }
+      this.observedEvents.push(eventToObserve);
     }
+
     for (const eventName of this.observedEvents) {
       this.on(eventName, this.pushEvent);
     }