async_await.cs

public interface IDataService
{
  Task<List<DataModel>> GetData();
}

[ApiController]
[Route("api/Test")]
public class TestController : ControllerBase
{
  private readonly IDataSerivce _dataService;
  
  public TestController(IDataService dataService)
  {
    _dataService = dataService;
  }
  
  public async Task<IActionResult> Get()
  {
    return Ok(await _dataService.GetData());
  }
}

public class given_an_instance_of_test_controller
{
  [Fact]
  public void assert_that_data_is_returned_from_get_call()
  {
    // arrange
    var dataServiceMock = new Mock<IDataService>();
    dataServiceMock.Setup(x => x.GetData()).ReturnsAsync(new List<DataModel> { new DataModel() } });
    var controller = new TestController();
    
    // act
    var result = controller.Get().GetAwaiter().GetResult() as OkObjectResult;
    
    // assert
    var resultValue = result.Value as List<DataModel>();
    Assert.NotNull(resultValue);
    Assert.IsTrue(resultValue.Any());
  }
}