public void GetBrandGroupByTest()
        {
            var x    = new LambdaExamples.FilterListOnMultipleColumns();
            var list = x.GroupByBrand();

            list.ShouldNotBeEmpty();
            list.First(c => c.Brand == "Nike").Count.ShouldBe(40);
            list.First(c => c.Brand == "Brooks").Count.ShouldBe(20);
            list.First(c => c.Brand == "Adidas").Count.ShouldBe(40);
        }