CSHARP-4057: Verify that issue is not present in LINQ3.

Author: rstam

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp4057Tests.cs

@@ -0,0 +1,96 @@
+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+using System.Linq;
+using FluentAssertions;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp4057Tests : Linq3IntegrationTest
+    {
+        [Fact]
+        public void Aggregate_Project_should_work()
+        {
+            var collection = CreateProductsCollection();
+
+            var aggregate = collection.Aggregate()
+               .Sort(Builders<Product>.Sort.Ascending(p => p.Id))
+               .Project(
+                    augmentedProductType => new ProductTypeSearchResult
+                    {
+                        IsExternalUrl = string.IsNullOrEmpty(augmentedProductType.ShopUrl ?? "")
+                    });
+
+            var stages = Translate(collection, aggregate);
+            AssertStages(
+                stages,
+                "{ $sort : { _id : 1 } }",
+                "{ $project : { IsExternalUrl : { $in : [{ $ifNull : ['$ShopUrl', ''] }, [null, '']] }, _id : 0 } }");
+
+            var results = aggregate.ToList();
+            results.Select(r => r.IsExternalUrl).Should().Equal(true, true, false);
+        }
+
+        [Fact]
+        public void Queryable_Select()
+        {
+            var collection = CreateProductsCollection();
+
+            var queryable = collection.AsQueryable()
+                .OrderBy(p => p.Id)
+                .Select(
+                    augmentedProductType => new ProductTypeSearchResult
+                    {
+                        IsExternalUrl = string.IsNullOrEmpty(augmentedProductType.ShopUrl ?? "")
+                    });
+
+            var stages = Translate(collection, queryable);
+            AssertStages(
+                stages,
+                "{ $sort : { _id : 1 } }",
+                "{ $project : { IsExternalUrl : { $in : [{ $ifNull : ['$ShopUrl', ''] }, [null, '']] }, _id : 0 } }");
+
+            var results = queryable.ToList();
+            results.Select(r => r.IsExternalUrl).Should().Equal(true, true, false);
+        }
+
+        private IMongoCollection<Product> CreateProductsCollection()
+        {
+            var collection = GetCollection<Product>();
+
+            var documents = new[]
+            {
+                new Product { Id = 1, ShopUrl = null },
+                new Product { Id = 2, ShopUrl = "" },
+                new Product { Id = 3, ShopUrl = "abc" }
+            };
+            CreateCollection(collection, documents);
+
+            return collection;
+        }
+
+        private class Product
+        {
+            public int Id { get; set; }
+            public string ShopUrl { get; set; }
+        }
+
+        private class ProductTypeSearchResult
+        {
+            public bool IsExternalUrl { get; set; }
+        }
+    }
+}