async method not returning when called from TestMethod

I am using Visual Studio 2013 and MSTest for unit testing my async method. I have async method as below:

    public async Task<Client> AddClientAsync(Client newClient)
    {
        newClient.ObjectState = ObjectState.Added;
        base.Insert(newClient);
        await unitOfWorkAsync.SaveChangesAsync();
        return newClient;
    }

I have written following unit test method to test it.

    [TestMethod]
    public async Task AddClientAsync_Success()
    {
        Client client = new Client()
        {
            Id=2,
            FirstName="John",
            LastName="Tylor",
            MaritalStatusId=1,
            RecordStatus=1                
        };

        var result = await clientAppService.AddClientAsync(client);
        Assert.IsNotNull(result);
    }

When I run/debug test case control reaches till below line and never returns. Its kind of getting stuck and keeps waiting endlessly at this line and test never completes.

await unitOfWorkAsync.SaveChangesAsync();

Any idea what am I missing here?