public void From()
{
var s = new Spec <Category>(x => x.Name == DbContextFixture.FirstCategoryName);
var from = s.From <Product>(x => x.Category);
var products = DbContext
.Products
.Include(x => x.Category)
.Where(from)
.ToList();
Assert.All(products, x =>
Assert.Equal(x.Category.Name, DbContextFixture.FirstCategoryName));
}