Actually add the test

spec/unit/ReEmitter.spec.ts

@@ -0,0 +1,49 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { EventEmitter } from "events";
+import { ReEmitter } from "../../src/ReEmitter";
+
+const EVENTNAME = "UnknownEntry";
+
+class EventSource extends EventEmitter {
+    doTheThing() {
+        this.emit(EVENTNAME, "foo", "bar");
+    }
+}
+
+class EventTarget extends EventEmitter {
+
+}
+
+describe("ReEmitter", function() {
+    it("Re-Emits events with the same args", function() {
+        const src = new EventSource();
+        const tgt = new EventTarget();
+
+        const handler = jest.fn();
+        tgt.on(EVENTNAME, handler);
+
+        const reEmitter = new ReEmitter(tgt);
+        reEmitter.reEmit(src, [EVENTNAME]);
+
+        src.doTheThing();
+
+        // Args should be the args passed to 'emit' after the event name, and
+        // also the source object of the event which re-emitter adds
+        expect(handler).toHaveBeenCalledWith("foo", "bar", src);
+    });
+});