Add support for T-Test aggregations

docs/aggregations.asciidoc

@@ -68,6 +68,8 @@ The values are typically extracted from the fields of the document (using the fi
 
 * <<top-metrics-aggregation-usage,Top Metrics Aggregation Usage>>
 
+* <<t-test-aggregation-usage,T Test Aggregation Usage>>
+
 * <<value-count-aggregation-usage,Value Count Aggregation Usage>>
 
 * <<weighted-average-aggregation-usage,Weighted Average Aggregation Usage>>
@@ -110,6 +112,8 @@ include::aggregations/metric/top-hits/top-hits-aggregation-usage.asciidoc[]
 
 include::aggregations/metric/top-metrics/top-metrics-aggregation-usage.asciidoc[]
 
+include::aggregations/metric/t-test/t-test-aggregation-usage.asciidoc[]
+
 include::aggregations/metric/value-count/value-count-aggregation-usage.asciidoc[]
 
 include::aggregations/metric/weighted-average/weighted-average-aggregation-usage.asciidoc[]

docs/aggregations/metric/t-test/t-test-aggregation-usage.asciidoc

@@ -0,0 +1,118 @@
+:ref_current: https://www.elastic.co/guide/en/elasticsearch/reference/master
+
+:github: https://github.com/elastic/elasticsearch-net
+
+:nuget: https://www.nuget.org/packages
+
+////
+IMPORTANT NOTE
+==============
+This file has been generated from https://github.com/elastic/elasticsearch-net/tree/master/src/Tests/Tests/Aggregations/Metric/TTest/TTestAggregationUsageTests.cs. 
+If you wish to submit a PR for any spelling mistakes, typos or grammatical errors for this file,
+please modify the original csharp file found at the link and submit the PR with that change. Thanks!
+////
+
+[[t-test-aggregation-usage]]
+=== T Test Aggregation Usage
+
+A t_test metrics aggregation that performs a statistical hypothesis test in which the test statistic follows a
+Student’s t-distribution under the null hypothesis on numeric values extracted from the aggregated documents or
+generated by provided scripts. In practice, this will tell you if the difference between two population means
+are statistically significant and did not occur by chance alone.
+
+NOTE: Available in Elasticsearch 7.8.0+ with at least basic license level
+
+Be sure to read the Elasticsearch documentation on {ref_current}/search-aggregations-metrics-ttest-aggregation.html[T-Test Aggregation].
+
+==== Fluent DSL example
+
+[source,csharp]
+----
+a => a
+.TTest("commits_visibility", c => c
+    .A(t => t
+        .Field(f => f.NumberOfCommits)
+        .Filter(f => f
+            .Term(ff => ff.Visibility, Visibility.Public)
+        )
+    )
+    .B(t => t
+        .Field(f => f.NumberOfCommits)
+        .Filter(f => f
+            .Term(ff => ff.Visibility, Visibility.Private)
+        )
+    )
+    .Type(TTestType.Heteroscedastic)
+)
+----
+
+==== Object Initializer syntax example
+
+[source,csharp]
+----
+new TTestAggregation("commits_visibility")
+{
+    A = new TTestPopulation
+    {
+        Field = Field<Project>(f => f.NumberOfCommits),
+        Filter = new TermQuery
+        {
+            Field = Field<Project>(f => f.Visibility),
+            Value = Visibility.Public
+        }
+    },
+    B = new TTestPopulation
+    {
+        Field = Field<Project>(f => f.NumberOfCommits),
+        Filter = new TermQuery
+        {
+            Field = Field<Project>(f => f.Visibility),
+            Value = Visibility.Private
+        }
+    },
+    Type = TTestType.Heteroscedastic
+}
+----
+
+[source,javascript]
+.Example json output
+----
+{
+  "commits_visibility": {
+    "t_test": {
+      "a": {
+        "field": "numberOfCommits",
+        "filter": {
+          "term": {
+            "visibility": {
+              "value": "Public"
+            }
+          }
+        }
+      },
+      "b": {
+        "field": "numberOfCommits",
+        "filter": {
+          "term": {
+            "visibility": {
+              "value": "Private"
+            }
+          }
+        }
+      },
+      "type": "heteroscedastic"
+    }
+  }
+}
+----
+
+==== Handling Responses
+
+[source,csharp]
+----
+response.ShouldBeValid();
+var tTest = response.Aggregations.TTest("commits_visibility");
+tTest.Should().NotBeNull();
+tTest.Value.Should().BeGreaterThan(0);
+----
+

src/Nest/Aggregations/AggregateDictionary.cs

@@ -244,6 +244,8 @@ public CompositeBucketAggregate Composite(string key)
 
 		public BoxplotAggregate Boxplot(string key) => TryGet<BoxplotAggregate>(key);
 
+		public ValueAggregate TTest(string key) => TryGet<ValueAggregate>(key);
+
 		private TAggregate TryGet<TAggregate>(string key) where TAggregate : class, IAggregate =>
 			BackingDictionary.TryGetValue(key, out var agg) ? agg as TAggregate : null;
 

src/Nest/Aggregations/AggregationContainer.cs

@@ -257,6 +257,10 @@ public interface IAggregationContainer
 		[DataMember(Name = "top_hits")]
 		ITopHitsAggregation TopHits { get; set; }
 
+		/// <inheritdoc cref="ITTestAggregation"/>
+		[DataMember(Name = "t_test")]
+		ITTestAggregation TTest { get; set; }
+
 		[DataMember(Name = "value_count")]
 		IValueCountAggregation ValueCount { get; set; }
 
@@ -387,6 +391,9 @@ public class AggregationContainer : IAggregationContainer
 		public ITermsAggregation Terms { get; set; }
 
 		public ITopHitsAggregation TopHits { get; set; }
+
+		public ITTestAggregation TTest { get; set; }
+
 		public IValueCountAggregation ValueCount { get; set; }
 
 		public IWeightedAverageAggregation WeightedAverage { get; set; }
@@ -542,6 +549,8 @@ public class AggregationContainerDescriptor<T> : DescriptorBase<AggregationConta
 
 		ITopHitsAggregation IAggregationContainer.TopHits { get; set; }
 
+		ITTestAggregation IAggregationContainer.TTest { get; set; }
+
 		IValueCountAggregation IAggregationContainer.ValueCount { get; set; }
 
 		IWeightedAverageAggregation IAggregationContainer.WeightedAverage { get; set; }
@@ -719,6 +728,12 @@ Func<TopHitsAggregationDescriptor<T>, ITopHitsAggregation> selector
 		) =>
 			_SetInnerAggregation(name, selector, (a, d) => a.TopHits = d);
 
+		/// <inheritdoc cref="ITTestAggregation"/>
+		public AggregationContainerDescriptor<T> TTest(string name,
+			Func<TTestAggregationDescriptor<T>, ITTestAggregation> selector
+		) =>
+			_SetInnerAggregation(name, selector, (a, d) => a.TTest = d);
+
 		public AggregationContainerDescriptor<T> Children<TChild>(string name,
 			Func<ChildrenAggregationDescriptor<TChild>, IChildrenAggregation> selector
 		) where TChild : class =>

src/Nest/Aggregations/Metric/TTest/TTestAggregation.cs

@@ -0,0 +1,120 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System;
+using System.Collections.Generic;
+using System.Runtime.Serialization;
+using Elasticsearch.Net;
+using Elasticsearch.Net.Utf8Json;
+
+namespace Nest
+{
+	/// <summary>
+	/// A metrics aggregation that performs a statistical hypothesis test in which the test statistic follows a
+	/// Student’s t-distribution under the null hypothesis on numeric values extracted from the aggregated documents or
+	/// generated by provided scripts. In practice, this will tell you if the difference between two population means
+	/// are statistically significant and did not occur by chance alone.
+	/// <para />
+	/// Available in Elasticsearch 7.8.0+ with at least basic license level
+	/// </summary>
+	[InterfaceDataContract]
+	[ReadAs(typeof(TTestAggregation))]
+	public interface ITTestAggregation : IAggregation
+	{
+		/// <summary>
+		/// T-test population A
+		/// </summary>
+		[DataMember(Name= "a")]
+		public ITTestPopulation A { get; set; }
+
+		/// <summary>
+		/// T-test population B
+		/// </summary>
+		[DataMember(Name= "b")]
+		public ITTestPopulation B { get; set; }
+
+		/// <summary>
+		/// T-test type
+		/// </summary>
+		[DataMember(Name = "type")]
+		public TTestType? Type { get; set; }
+	}
+
+	/// <inheritdoc cref="ITTestAggregation" />
+	public class TTestAggregation : AggregationBase, ITTestAggregation
+	{
+		internal TTestAggregation() { }
+
+		public TTestAggregation(string name) : base(name) { }
+
+		internal override void WrapInContainer(AggregationContainer c) => c.TTest = this;
+
+		/// <inheritdoc />
+		public ITTestPopulation A { get; set; }
+		/// <inheritdoc />
+		public ITTestPopulation B { get; set; }
+		/// <inheritdoc />
+		public TTestType? Type { get; set; }
+	}
+
+	/// <inheritdoc cref="ITTestAggregation" />
+	public class TTestAggregationDescriptor<T>
+		: DescriptorBase<TTestAggregationDescriptor<T>, ITTestAggregation>, ITTestAggregation
+		where T : class
+	{
+		IDictionary<string, object> IAggregation.Meta { get; set; }
+		string IAggregation.Name { get; set; }
+		ITTestPopulation ITTestAggregation.A { get; set; }
+		ITTestPopulation ITTestAggregation.B { get; set; }
+		TTestType? ITTestAggregation.Type { get; set; }
+
+		/// <inheritdoc cref="ITTestAggregation.A"/>
+		public TTestAggregationDescriptor<T> A(Func<TTestPopulationDescriptor<T>, ITTestPopulation> selector) =>
+			Assign(selector, (a, v) => a.A = v?.Invoke(new TTestPopulationDescriptor<T>()));
+
+		/// <inheritdoc cref="ITTestAggregation.A"/>
+		public TTestAggregationDescriptor<T> A<TOther>(Func<TTestPopulationDescriptor<TOther>, ITTestPopulation> selector) where TOther : class =>
+			Assign(selector, (a, v) => a.A = v?.Invoke(new TTestPopulationDescriptor<TOther>()));
+
+		/// <inheritdoc cref="ITTestAggregation.B"/>
+		public TTestAggregationDescriptor<T> B(Func<TTestPopulationDescriptor<T>, ITTestPopulation> selector) =>
+			Assign(selector, (a, v) => a.B = v?.Invoke(new TTestPopulationDescriptor<T>()));
+
+		/// <inheritdoc cref="ITTestAggregation.B"/>
+		public TTestAggregationDescriptor<T> B<TOther>(Func<TTestPopulationDescriptor<TOther>, ITTestPopulation> selector) where TOther : class =>
+			Assign(selector, (a, v) => a.B = v?.Invoke(new TTestPopulationDescriptor<TOther>()));
+
+		/// <inheritdoc cref="ITTestAggregation.Type"/>
+		public TTestAggregationDescriptor<T> Type(TTestType? type) => Assign(type, (a, v) => a.Type = v);
+
+		/// <inheritdoc cref="IAggregation.Meta"/>
+		public TTestAggregationDescriptor<T> Meta(Func<FluentDictionary<string, object>, FluentDictionary<string, object>> selector) =>
+			Assign(selector, (a, v) => a.Meta = v?.Invoke(new FluentDictionary<string, object>()));
+	}
+
+	/// <summary>
+	/// The type of t-test
+	/// </summary>
+	[StringEnum]
+	public enum TTestType
+	{
+		/// <summary>
+		/// performs paired t-test
+		/// </summary>
+		[EnumMember(Value = "paired")]
+		Paired,
+
+		/// <summary>
+		/// performs two-sample equal variance test
+		/// </summary>
+		[EnumMember(Value = "homoscedastic")]
+		Homoscedastic,
+
+		/// <summary>
+		/// performs two-sample unequal variance test (this is default)
+		/// </summary>
+		[EnumMember(Value = "heteroscedastic")]
+		Heteroscedastic,
+	}
+}

src/Nest/Aggregations/Metric/TTest/TTestGroup.cs

@@ -0,0 +1,74 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
+using System;
+using System.Linq.Expressions;
+using System.Runtime.Serialization;
+using Elasticsearch.Net.Utf8Json;
+
+namespace Nest
+{
+	/// <summary>
+	/// A population for a <see cref="TTestAggregation"/>
+	/// </summary>
+	[InterfaceDataContract]
+	[ReadAs(typeof(TTestPopulation))]
+	public interface ITTestPopulation
+	{
+		/// <summary>
+		/// The field to use for the population values. Must be a numeric field.
+		/// </summary>
+		[DataMember(Name = "field")]
+		Field Field { get; set; }
+
+		/// <summary>
+		/// A script tp use to calculate population values.
+		/// </summary>
+		[DataMember(Name = "script")]
+		IScript Script { get; set; }
+
+		/// <summary>
+		/// A filter to apply to target field to filter population values. Useful
+		/// when two populations use the same field for values, to filter the values.
+		/// </summary>
+		[DataMember(Name = "filter")]
+		QueryContainer Filter { get; set; }
+	}
+
+	/// <inheritdoc />
+	public class TTestPopulation : ITTestPopulation
+	{
+		/// <inheritdoc />
+		public Field Field { get; set; }
+		/// <inheritdoc />
+		public IScript Script { get; set; }
+		/// <inheritdoc />
+		public QueryContainer Filter { get; set; }
+	}
+
+	/// <inheritdoc cref="ITTestPopulation"/>
+	public class TTestPopulationDescriptor<T> : DescriptorBase<TTestPopulationDescriptor<T>, ITTestPopulation>, ITTestPopulation where T : class
+	{
+		Field ITTestPopulation.Field { get; set; }
+		IScript ITTestPopulation.Script { get; set; }
+		QueryContainer ITTestPopulation.Filter { get; set; }
+
+		/// <inheritdoc cref="ITTestPopulation.Field"/>
+		public TTestPopulationDescriptor<T> Field(Field field) => Assign(field, (a, v) => a.Field = v);
+
+		/// <inheritdoc cref="ITTestPopulation.Field"/>
+		public TTestPopulationDescriptor<T> Field<TValue>(Expression<Func<T, TValue>> field) => Assign(field, (a, v) => a.Field = v);
+
+		/// <inheritdoc cref="ITTestPopulation.Script"/>
+		public TTestPopulationDescriptor<T> Script(string script) => Assign((InlineScript)script, (a, v) => a.Script = v);
+
+		/// <inheritdoc cref="ITTestPopulation.Script"/>
+		public TTestPopulationDescriptor<T> Script(Func<ScriptDescriptor, IScript> scriptSelector) =>
+			Assign(scriptSelector, (a, v) => a.Script = v?.Invoke(new ScriptDescriptor()));
+
+		/// <inheritdoc cref="ITTestPopulation.Filter"/>
+		public TTestPopulationDescriptor<T> Filter(Func<QueryContainerDescriptor<T>, QueryContainer> filter) =>
+			Assign(filter, (a, v) => a.Filter = v?.Invoke(new QueryContainerDescriptor<T>()));
+	}
+}

src/Nest/Aggregations/Metric/ValueAggregate.cs

@@ -2,7 +2,7 @@
 // Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information
 
-namespace Nest
+namespace Nest
 {
 	public class ValueAggregate : MetricAggregateBase
 	{