Address PR comments

src/Nest/Aggregations/Aggregate.cs

@@ -3,12 +3,15 @@
 namespace Nest
 {
 	/// <summary>
-	/// Represents the result of an aggregation on the response
+	/// Aggregation response for an aggregation request
 	/// </summary>
 	[ExactContractJsonConverter(typeof(AggregateJsonConverter))]
 	public interface IAggregate
 	{
 		//TODO this public set is problematic
+		/// <summary>
+		/// Metadata for the aggregation
+		/// </summary>
 		IReadOnlyDictionary<string, object> Meta { get; set; }
 	}
 }

src/Nest/Aggregations/AggregateDictionary.cs

@@ -179,11 +179,11 @@ public CompositeBucketAggregate Composite(string key)
 		{
 			var bucket = this.TryGet<BucketAggregate>(key);
 			if (bucket == null) return null;
-			return new CompositeBucketAggregate()
+			return new CompositeBucketAggregate
 			{
 				Buckets = bucket.Items.OfType<CompositeBucket>().ToList(),
 				Meta = bucket.Meta,
-				AfterKey = bucket.AfterKey
+				AfterKey = new CompositeKey(bucket.AfterKey)
 			};
 		}
 

src/Nest/Aggregations/Bucket/BucketAggregate.cs

@@ -23,32 +23,43 @@ public SingleBucketAggregate(IReadOnlyDictionary<string, IAggregate> aggregation
 		[Obsolete("Use methods on this instance to access sub aggregations. Will be removed in NEST 7.x")]
 		public AggregateDictionary Aggregations { get; protected internal set; }
 
+		/// <summary>
+		/// Count of documents in the bucket
+		/// </summary>
 		public long DocCount { get; internal set; }
 	}
 
+	/// <summary>
+	/// Aggregation response for a bucket aggregation
+	/// </summary>
+	/// <typeparam name="TBucket"></typeparam>
 	public class MultiBucketAggregate<TBucket> : IAggregate
 		where TBucket : IBucket
 	{
+		/// <inheritdoc />
 		public IReadOnlyDictionary<string, object> Meta { get; set; }
 
+		/// <summary>
+		/// The buckets into which results are grouped
+		/// </summary>
 		public IReadOnlyCollection<TBucket> Buckets { get; set; } = EmptyReadOnly<TBucket>.Collection;
 	}
 
-	public class CompositeBucketAggregate : IAggregate
+	/// <summary>
+	/// Aggregation response of <see cref="CompositeAggregation"/>
+	/// </summary>
+	public class CompositeBucketAggregate : MultiBucketAggregate<CompositeBucket>
 	{
-		public IReadOnlyDictionary<string, object> Meta { get; set; }
-
-		public IReadOnlyCollection<CompositeBucket> Buckets { get; set; } = EmptyReadOnly<CompositeBucket>.Collection;
-
 		/// <summary>
-		/// The after_key is equals to the last bucket returned in the response before any filtering that could be done by Pipeline aggregations.
-		/// If all buckets are filtered/removed by a pipeline aggregation, the after_key will contain the last bucket before filtering.
+		/// The composite key of the last bucket returned
+		/// in the response before any filtering by pipeline aggregations.
+		/// If all buckets are filtered/removed by pipeline aggregations,
+		/// <see cref="AfterKey"/> will contain the composite key of the last bucket before filtering.
 		/// </summary>
 		/// <remarks> Valid for Elasticsearch 6.3.0+ </remarks>
-		public IReadOnlyDictionary<string, object> AfterKey { get; set; } = EmptyReadOnly<string, object>.Dictionary;
+		public CompositeKey AfterKey { get; set; }
 	}
 
-
 	// Intermediate object used for deserialization
 	public class BucketAggregate : IAggregate
 	{

src/Tests/Tests/Framework/EndpointTests/ApiIntegrationTestBase.cs

@@ -32,13 +32,13 @@ protected ApiIntegrationTestBase(TCluster cluster, EndpointUsage usage) : base(c
 		public override IElasticClient Client => this.Cluster.Client;
 		protected override TInitializer Initializer => Activator.CreateInstance<TInitializer>();
 
-		[I] public virtual async Task ReturnsExpectedStatusCode() =>
+		[I] public async Task ReturnsExpectedStatusCode() =>
 			await this.AssertOnAllResponses(r => r.ApiCall.HttpStatusCode.Should().Be(this.ExpectStatusCode));
 
-		[I] public virtual async Task ReturnsExpectedIsValid() =>
+		[I] public async Task ReturnsExpectedIsValid() =>
 			await this.AssertOnAllResponses(r => r.ShouldHaveExpectedIsValid(this.ExpectIsValid));
 
-		[I] public virtual async Task ReturnsExpectedResponse() => await this.AssertOnAllResponses(ExpectResponse);
+		[I] public async Task ReturnsExpectedResponse() => await this.AssertOnAllResponses(ExpectResponse);
 
 		protected override Task AssertOnAllResponses(Action<TResponse> assert)
 		{

src/Tests/Tests/Tests.csproj

@@ -7,7 +7,7 @@
     <NoWarn>$(NoWarn);xUnit1013</NoWarn>
   </PropertyGroup>
   <ItemGroup>
-    <DotNetCliToolReference Include="dotnet-xunit" Version="2.3.0-beta1-build3642" />
+    <DotNetCliToolReference Include="dotnet-xunit" Version="2.3.1" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Tests.Core\Tests.Core.csproj" />