diff --git a/src/utilities/observables/Concast.ts b/src/utilities/observables/Concast.ts
index 5c32a15e046..59c1c9b61a1 100644
--- a/src/utilities/observables/Concast.ts
+++ b/src/utilities/observables/Concast.ts
@@ -212,11 +212,7 @@ export class Concast<T> extends Observable<T> {
         } else if (isPromiseLike(value)) {
           value.then(
             (obs) => (this.sub = obs.subscribe(this.handlers)),
-            () => {
-              // add error handler here to silence unhandled promise rejection
-              // so the tests can run at all, but do not fix yet
-              // to show the memory leak
-            }
+            this.handlers.error
           );
         } else {
           this.sub = value.subscribe(this.handlers);
diff --git a/src/utilities/observables/__tests__/Concast.ts b/src/utilities/observables/__tests__/Concast.ts
index a25277ed4b5..e52b55022b7 100644
--- a/src/utilities/observables/__tests__/Concast.ts
+++ b/src/utilities/observables/__tests__/Concast.ts
@@ -207,7 +207,7 @@ describe("Concast Observable (similar to Behavior Subject in RxJS)", () => {
     await expect(observerRefs[0]).toBeGarbageCollected();
   });
 
-  it.failing("rejecting a source-wrapping promise of a concast frees all observer references on `this.observers`", async () => {
+  it("rejecting a source-wrapping promise of a concast frees all observer references on `this.observers`", async () => {
     const { promise, reject } = deferred<Observable<number>>();
     const observers: Observer<any>[] = [{ next() {}, error() {} }];
     const observerRefs = observers.map((observer) => new WeakRef(observer));
@@ -268,7 +268,7 @@ describe("Concast Observable (similar to Behavior Subject in RxJS)", () => {
     await expect(observerRefs[0]).toBeGarbageCollected();
   });
 
-  it.failing("after subscribing to an already-rejected concast, the reference is freed up again", async () => {
+  it("after subscribing to an already-rejected concast, the reference is freed up again", async () => {
     const concast = new Concast<number>([Promise.reject("error")]);
     await expect(concast.promise).rejects.toBe("error");
     await Promise.resolve();
diff --git a/tsconfig.tests.json b/tsconfig.tests.json
index d6bb25bd3fd..45c0454886a 100644
--- a/tsconfig.tests.json
+++ b/tsconfig.tests.json
@@ -1,5 +1,8 @@
 {
   "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "lib": ["es2015", "esnext.asynciterable", "dom", "ES2021.WeakRef"],
+  },
   "include": ["src/**/__tests__/**/*.ts", "src/**/__tests__/**/*.tsx"],
   "exclude": []
 }