public void TestMultiplyAsyncException(int a, int b)
        {
            AsyncUtil obj = new AsyncUtil();

            Assert.ThrowsAsync <InvalidOperationException>(async() => await obj.MultiplyAsync(a, b));
        }
        public async Task <int> TestMultiplyAsync(int a, int b)
        {
            AsyncUtil obj = new AsyncUtil();

            return(await obj.MultiplyAsync(a, b));
        }