public async Task GetArtistsAsync_Given_Artists_In_DB_Exist_Should_Return_Collection_Of_Artists()
{
IEnumerable <Artist> artists = new List <Artist>()
{
new Artist(),
new Artist(),
new Artist(),
new Artist()
};
string artistName = null;
artistManager
.Setup(s => s.GetAllArtistsAsync())
.Returns(Task.FromResult(artists));
var retval = await _artistController.GetArtistsAsync(artistName) as OkObjectResult;
Assert.IsNotNull(retval.Value);
}