aggregate testings.

PoweredSoft.DynamicQuery.Test/AggregateInterceptorTests.cs

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+using PoweredSoft.DynamicQuery.Core;
+using PoweredSoft.DynamicQuery.Test.Mock;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Xunit;
+
+namespace PoweredSoft.DynamicQuery.Test
+{
+    public class AggregateInterceptorTests
+    {
+        private class MockAggregateInterceptor : IAggregateInterceptor
+        {
+            public IAggregate InterceptAggregate(IAggregate aggregate) => new Aggregate
+            {
+                Path = "Item.Price",
+                Type = AggregateType.Avg
+            };
+        }
+
+        [Fact]
+        public void Simple()
+        {
+            MockContextFactory.SeedAndTestContextFor("AggregatorInterceptorTests_Simple", TestSeeders.SimpleSeedScenario, ctx =>
+            {
+                var expected = ctx.OrderItems.GroupBy(t => true).Select(t => new
+                {
+                    PriceAtTheTime = t.Average(t2 => t2.Item.Price)
+                }).First();
+
+                var criteria = new QueryCriteria();
+                criteria.Aggregates.Add(new Aggregate
+                {
+                    Type = AggregateType.Avg,
+                    Path = "ItemPrice"
+                });
+                var queryHandler = new QueryHandler();
+                queryHandler.AddInterceptor(new MockAggregateInterceptor());
+                var result = queryHandler.Execute(ctx.OrderItems, criteria);
+                Assert.Equal(expected.PriceAtTheTime, result.Aggregates.First().Value);
+            });
+        }
+    }
+}