CSHARP-3037: Correct types in ArgumentException message.

Author: kevbite

src/MongoDB.Driver/PipelineDefinition.cs

@@ -332,34 +332,29 @@ public override RenderedPipelineDefinition<TOutput> Render(IBsonSerializer<TInpu
 
         private static List<IPipelineStageDefinition> VerifyStages(List<IPipelineStageDefinition> stages)
         {
-            var nextInputType = typeof(TInput);
+            var expectedInputType = typeof(TInput);
             for (int i = 0; i < stages.Count; i++)
             {
-                if (stages[i].InputType != nextInputType)
+                if (stages[i].InputType != expectedInputType)
                 {
-                    var message = string.Format(
-                        "The input type to stage[{0}] was expected to be {1}, but was {2}.",
-                        i,
-                        nextInputType,
-                        stages[i].InputType);
-                    throw new ArgumentException(message, "stages");
+                    var message =
+                        $"The input type to stage[{i}] was expected to be {expectedInputType}, but was {stages[i].InputType}.";
+                    throw new ArgumentException(message, nameof(stages));
                 }
 
-                nextInputType = stages[i].OutputType;
+                expectedInputType = stages[i].OutputType;
             }
+            var lastStageOutputType = expectedInputType;
 
-            if (nextInputType != typeof(TOutput))
+            if (lastStageOutputType != typeof(TOutput))
             {
-                var message = string.Format(
-                    "The output type to the last stage was expected to be {0}, but was {1}.",
-                    nextInputType,
-                    stages.Last().OutputType);
-                throw new ArgumentException(message, "stages");
+                var message =
+                    $"The output type to the last stage was expected to be {typeof(TOutput)}, but was {lastStageOutputType}.";
+                throw new ArgumentException(message, nameof(stages));
             }
 
             return stages;
         }
-    }
 
     internal class OptimizingPipelineDefinition<TInput, TOutput> : PipelineDefinition<TInput, TOutput>
     {
@@ -380,7 +375,7 @@ public override RenderedPipelineDefinition<TOutput> Render(IBsonSerializer<TInpu
         {
             var rendered = _wrapped.Render(inputSerializer, serializerRegistry);
 
-            // do some combining of $match documents if possible. This is optimized for the 
+            // do some combining of $match documents if possible. This is optimized for the
             // OfType case where we've added a discriminator as a match at the beginning of the pipeline.
             if (rendered.Documents.Count > 1)
             {
@@ -401,4 +396,4 @@ public override RenderedPipelineDefinition<TOutput> Render(IBsonSerializer<TInpu
             return rendered;
         }
     }
-}
+}

tests/MongoDB.Driver.Tests/PipelineDefinitionTests.cs

@@ -25,24 +25,43 @@ namespace MongoDB.Driver.Tests
     public class PipelineStagePipelineDefinitionTests
     {
         [Fact]
-        public void Constructor_should_verify_the_inputs_and_outputs_of_the_stages_and_throw_when_invalid()
+        public void Constructor_should_verify_the_inputs_and_outputs_of_the_stages_and_throw_when_intermediate_stage_is_invalid()
         {
-            var stages = new IPipelineStageDefinition[] 
+            var stages = new IPipelineStageDefinition[]
             {
                 new BsonDocumentPipelineStageDefinition<Person, BsonDocument>(new BsonDocument()),
                 new BsonDocumentPipelineStageDefinition<BsonDocument, Pet>(new BsonDocument()),
                 new BsonDocumentPipelineStageDefinition<BsonDocument, Person>(new BsonDocument())
             };
 
-            Action act = () => new PipelineStagePipelineDefinition<Person, Person>(stages);
+            var exception = Record.Exception(() => new PipelineStagePipelineDefinition<Person, Person>(stages));
 
-            act.ShouldThrow<ArgumentException>();
+            var e = exception.Should().BeOfType<ArgumentException>().Subject;
+            e.ParamName.Should().Be("stages");
+            e.Message.Should().Contain($"The input type to stage[2] was expected to be {typeof(Pet)}, but was {typeof(BsonDocument)}.");
         }
 
+        [Fact]
+        public void Constructor_should_verify_the_inputs_and_outputs_of_the_stages_and_throw_when_final_stage_is_invalid()
+        {
+            var stages = new IPipelineStageDefinition[]
+            {
+                new BsonDocumentPipelineStageDefinition<Person, BsonDocument>(new BsonDocument()),
+                new BsonDocumentPipelineStageDefinition<BsonDocument, Pet>(new BsonDocument()),
+                new BsonDocumentPipelineStageDefinition<Pet, BsonDocument>(new BsonDocument())
+            };
+
+            var exception = Record.Exception(() => new PipelineStagePipelineDefinition<Person, Person>(stages));
+
+            var e = exception.Should().BeOfType<ArgumentException>().Subject;
+            e.ParamName.Should().Be("stages");
+            e.Message.Should().Contain($"The output type to the last stage was expected to be {typeof(Person)}, but was {typeof(BsonDocument)}.");
+       }
+
         [Fact]
         public void Constructor_should_verify_the_inputs_and_outputs_of_the_stages()
         {
-            var stages = new IPipelineStageDefinition[] 
+            var stages = new IPipelineStageDefinition[]
             {
                 new BsonDocumentPipelineStageDefinition<Person, BsonDocument>(new BsonDocument()),
                 new BsonDocumentPipelineStageDefinition<BsonDocument, Pet>(new BsonDocument()),
@@ -71,7 +90,7 @@ private class Person
         {
             [BsonElement("fn")]
             public string FirstName { get; set; }
-        
+
             [BsonElement("pets")]
             public Pet[] Pets { get; set; }
         }
@@ -80,6 +99,6 @@ private class Pet
         {
             [BsonElement("name")]
             public string Name { get; set; }
-        }    
+        }
     }
 }