public async Task ItADivideTwoNumbers()
{
Mock <IRepository <Operation> > repository = new Mock <IRepository <Operation> >();
OperationService operationService = new OperationService(repository.Object);
Operation result = await operationService.Div(null, 10, 2);
Assert.Equal(OperationType.Division, result.OperationType);
Assert.Equal(5, result.Result);
}