using Moq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Threading.Tasks;
using System.Diagnostics.CodeAnalysis;

namespace LibraryTest
{
    [TestClass]
    public class ApplicationTest
    {
        [TestMethod]
    public async Task GetDataFromDataBase_Returns_True()
    {

            IApplication classUnderTest = new Application();
            var result = await classUnderTest.GetDataFromDataBase();
            Assert.IsTrue(result);
    }
    }
 }

/////////   Actual Class library
using System;

namespace Library
{
    public class Application : IApplication
    {
        public virtual async Task<bool> GetDataFromDataBase()
        {
            //if data retrive successfull, return true, else false
            return true;
        }
    }
    public interface IApplication
    {
        Task<bool> GetDataFromDataBase();
    }
}