Throwing a custom error in a TypeScript promise

error.ts

export class RddiError extends Error {
    constructor(public status: number) {
        super();
    }    
}

export class TestHarness {
    public async errorFunction(): Promise<void> {
        throw new RddiError(12);
    }

    public async runAsync(): Promise<void> {
        try {
            await this.errorFunction();
        } catch(error) {
            if (error instanceof RddiError) {
                console.log(error.status);
            } else {
                console.log("unknown error thrown!");
            }
        }
    }

    public runPromise(): Promise<void> {
        return this.errorFunction()
        .then(() => console.log("won't happen"))
        .catch(error => {
            if (error instanceof RddiError) {
                console.log(error.status);
            } else {
                console.log("unknown error thrown!");
            }
        });
    }
}