Some additional tests and a bit of refactoring

src/EntityFrameworkCore.Projections/Infrastructure/Internal/CustomQueryTranslationPreprocessorFactory.cs

@@ -13,7 +13,7 @@ namespace EntityFrameworkCore.Projections.Infrastructure.Internal
     {
         readonly IQueryTranslationPreprocessorFactory _decoratedFactory;
         readonly QueryTranslationPreprocessorDependencies _queryTranslationPreprocessorDependencies;
-        readonly ProjectableExpressionReplacer _projectableExpressionReplacer = new();
+        readonly ProjectableExpressionReplacer _projectableExpressionReplacer = new(new ProjectionExpressionResolver());
 
         public CustomQueryTranslationPreprocessorFactory(IQueryTranslationPreprocessorFactory decoratedFactory, QueryTranslationPreprocessorDependencies queryTranslationPreprocessorDependencies)
         {

src/EntityFrameworkCore.Projections/Services/ExpressionArgumentReplacer.cs

@@ -7,7 +7,7 @@ using System.Threading.Tasks;
 
 namespace EntityFrameworkCore.Projections.Services
 {
-    public class ExpressionArgumentReplacer : ExpressionVisitor
+    public sealed class ExpressionArgumentReplacer : ExpressionVisitor
     {
         readonly IEnumerable<(ParameterExpression parameter, Expression argument)>? _parameterArgumentMapping;
 

src/EntityFrameworkCore.Projections/Services/IProjectionExpressionResolver.cs

@@ -0,0 +1,10 @@
+using System.Linq.Expressions;
+using System.Reflection;
+
+namespace EntityFrameworkCore.Projections.Services
+{
+    public interface IProjectionExpressionResolver
+    {
+        LambdaExpression FindGeneratedExpression(MemberInfo projectableMemberInfo);
+    }
+}

src/EntityFrameworkCore.Projections/Services/ParameterExtractor.cs

@@ -1,28 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Linq.Expressions;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace EntityFrameworkCore.Projections.Services
-{
-    public sealed class ParameterExtractor : ExpressionVisitor
-    {
-        List<ParameterExpression>? _extractedParameters = null;
-
-        protected override Expression VisitParameter(ParameterExpression node)
-        {
-            if (_extractedParameters is null)
-            {
-                _extractedParameters = new List<ParameterExpression>();
-            }
-
-            _extractedParameters.Add(node);
-            return base.VisitParameter(node);
-        }
-
-        public IEnumerable<ParameterExpression> ExtractedParameters
-            => _extractedParameters ?? Enumerable.Empty<ParameterExpression>();
-    }
-}

src/EntityFrameworkCore.Projections/Services/ProjectableExpressionReplacer.cs

@@ -7,13 +7,18 @@ using System.Threading.Tasks;
 
 namespace EntityFrameworkCore.Projections.Services
 {
-    public class ProjectableExpressionReplacer : ExpressionVisitor
+    public sealed class ProjectableExpressionReplacer : ExpressionVisitor
     {
-        readonly ProjectionExpressionResolver _resolver = new();
+        readonly IProjectionExpressionResolver _resolver;
+
+        public ProjectableExpressionReplacer(IProjectionExpressionResolver projectionExpressionResolver)
+        {
+            _resolver = projectionExpressionResolver;
+        }
 
         protected override Expression VisitMethodCall(MethodCallExpression node)
         {
-            if (node.Method.GetCustomAttributes(true).OfType<ProjectableAttribute>().Any())
+            if (node.Method.GetCustomAttributes(false).OfType<ProjectableAttribute>().Any())
             {
                 var reflectedExpression = _resolver.FindGeneratedExpression(node.Method);
 

src/EntityFrameworkCore.Projections/Services/ProjectionExpressionResolver.cs

@@ -10,7 +10,7 @@ using EntityFrameworkCore.Projections.Extensions;
 
 namespace EntityFrameworkCore.Projections.Services
 {
-    public sealed class ProjectionExpressionResolver
+    public sealed class ProjectionExpressionResolver : IProjectionExpressionResolver
     {
         readonly ConcurrentDictionary<string, LambdaExpression> _lookupCache = new();
 
@@ -36,7 +36,7 @@ namespace EntityFrameworkCore.Projections.Services
                 }
 
                 return expressionFactoryMethod.Invoke(null, null) as LambdaExpression ?? throw new InvalidOperationException("Expected lambda");
-            }); 
+            });
         }
     }
 }