diff --git a/src/index.ts b/src/index.ts
index 8020c9f..95f3bd4 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -14,7 +14,7 @@ class AbortableEmittery extends Emittery {
 export default class AbortablePromise<T> implements Promise<T | null> {
   private emitter: AbortableEmittery;
 
-  private result_promise: Promise<T>;
+  private result_promise: Promise<T | null>;
   private fulfilled = false;
   private result: T;
 
@@ -33,7 +33,7 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     function await_or_abort<L = any>(
       promise: Promise<L> | AbortablePromise<L>,
       on_abort?: () => Promise<unknown> | void
-    ): Promise<L> {
+    ): Promise<L | null> {
       console.log("await_or_abort", promise);
       if (promise instanceof AbortablePromise && !on_abort) {
         on_abort = async () => promise.abort();
@@ -86,6 +86,10 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     this.emitter.abort();
   }
 
+  get [Symbol.toStringTag]() {
+    return "AbortablePromise";
+  }
+
   then<TResult1 = T, TResult2 = never>(
     onfulfilled?:
       | ((value: T) => TResult1 | PromiseLike<TResult1>)
@@ -99,7 +103,7 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     const self = this;
     return new AbortablePromise(async function* (await_or_abort) {
       if (self.fulfilled) {
-        onfulfilled(self.result);
+        onfulfilled && onfulfilled(self.result);
         return;
       }
       const ret = await await_or_abort(self.result_promise, () => {
@@ -107,7 +111,7 @@ export default class AbortablePromise<T> implements Promise<T | null> {
       });
       yield;
       if (onfulfilled) {
-        onfulfilled(ret);
+        onfulfilled(ret as T);
       }
     });
   }
@@ -127,13 +131,21 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     });
   }
 
+  finally(onfinally?: (() => void) | undefined | null): AbortablePromise<T> {
+    const self = this;
+    return new AbortablePromise(async function* (await_or_abort) {
+      await await_or_abort(self);
+      onfinally && onfinally();
+    });
+  }
+
   static deadlyRace<L>(
     promises: AbortablePromise<L>[],
     should_kill_others: (arg: L) => Promise<boolean> = async () => true
   ): Promise<L> {
     return new AbortablePromise(async function* (await_or_abort) {
       return await_or_abort(
-        new Promise((resolve, reject) => {
+        new Promise((resolve, _) => {
           let resolved = false;
           const callback = async (arg: L) => {
             if (resolved) return;
@@ -156,55 +168,3 @@ export default class AbortablePromise<T> implements Promise<T | null> {
     });
   }
 }
-
-const sleep = promisify((timeout: number, callback: (...args: any[]) => void) =>
-  setTimeout(callback, timeout)
-);
-
-// const a = new AbortablePromise(async function* () {
-//   yield await sleep(1000);
-//   console.log("awaited 100");
-//   yield await sleep(2000);
-//   console.log("awaited 200");
-//   yield await sleep(3000);
-//   console.log("awaited 300");
-// });
-//
-// const a = new AbortablePromise(async function* () {
-//   yield await sleep(1000);
-//   console.log("awaited 100");
-//   yield await sleep(2000);
-//   console.log("awaited 200");
-//   yield await sleep(3000);
-//   console.log("awaited 300");
-// });
-
-// function abortableSleep(ms: number): AbortablePromise<void> {
-//   return new AbortablePromise(async function* () {
-//     await sleep(ms);
-//     yield;
-//     console.log(`Slept ${ms}.`);
-//   });
-// }
-
-// const b = AbortablePromise.deadlyRace([
-//   abortableSleep(1000),
-//   abortableSleep(2000),
-//   abortableSleep(3000),
-// ]);
-
-// setTimeout(() => a.abort(), 1500);
-
-// const b = new AbortablePromise(async function* (await_or_abort) {
-//   const ping = await deferedSpawn("ping", ["8.8.8.8"]);
-//   while (true) {
-//     console.log(
-//       await await_or_abort(ping.waitForNextData(), () => {
-//         ping.kill();
-//       })
-//     );
-//     yield;
-//   }
-// });
-
-// setTimeout(() => b.abort(), 5000);
diff --git a/src/test.ts b/src/test.ts
new file mode 100644
index 0000000..b3dd59b
--- /dev/null
+++ b/src/test.ts
@@ -0,0 +1,45 @@
+import { promisify } from "util";
+import AbortablePromise from ".";
+
+const sleep = promisify((timeout: number, callback: (...args: any[]) => void) =>
+  setTimeout(callback, timeout)
+);
+
+const a = new AbortablePromise(async function* () {
+  yield await sleep(1000);
+  console.log("awaited 100");
+  yield await sleep(2000);
+  console.log("awaited 200");
+  yield await sleep(3000);
+  console.log("awaited 300");
+});
+
+setTimeout(() => a.abort(), 1500);
+
+function abortableSleep(ms: number): AbortablePromise<void> {
+  return new AbortablePromise(async function* () {
+    await sleep(ms);
+    yield;
+    console.log(`Slept ${ms}.`);
+  });
+}
+
+const b = AbortablePromise.deadlyRace([
+  abortableSleep(1000),
+  abortableSleep(2000),
+  abortableSleep(3000),
+]);
+
+// const b = new AbortablePromise(async function* (await_or_abort) {
+//   const ping = await deferedSpawn("ping", ["8.8.8.8"]);
+//   while (true) {
+//     console.log(
+//       await await_or_abort(ping.waitForNextData(), () => {
+//         ping.kill();
+//       })
+//     );
+//     yield;
+//   }
+// });
+
+// setTimeout(() => b.abort(), 5000);