Minor metric fixes (#3159)

src/OpenTelemetry/Metrics/MeterProviderBuilderBase.cs

@@ -25,7 +25,8 @@ using OpenTelemetry.Resources;
 namespace OpenTelemetry.Metrics
 {
     /// <summary>
-    /// Build MeterProvider with Resource, Readers, and Instrumentation.
+    /// Build MeterProvider with Instrumentations, Meters,
+    /// Resource, Readers, and Views.
     /// </summary>
     public abstract class MeterProviderBuilderBase : MeterProviderBuilder
     {

src/OpenTelemetry/Metrics/MeterProviderExtensions.cs

@@ -106,6 +106,13 @@ namespace OpenTelemetry.Metrics
             return true;
         }
 
+        /// <summary>
+        /// Finds the Metric exporter of the given type from the provider.
+        /// </summary>
+        /// <typeparam name="T">The type of the Exporter.</typeparam>
+        /// <param name="provider">The MeterProvider from which Exporter should be found.</param>
+        /// <param name="exporter">The exporter instance.</param>
+        /// <returns>true if the exporter of specified Type is found; otherwise false.</returns>
         public static bool TryFindExporter<T>(this MeterProvider provider, out T exporter)
             where T : BaseExporter<Metric>
         {

src/OpenTelemetry/Metrics/MetricStreamConfiguration.cs

@@ -71,7 +71,8 @@ namespace OpenTelemetry.Metrics
         /// <item>If not provided, all the tags provided by the instrument
         /// while reporting measurements will be used for aggregation.
         /// If provided, only those tags in this list will be used
-        /// for aggregation.
+        /// for aggregation. Providing an empty array will result
+        /// in a metric stream without any tags.
         /// </item>
         /// <item>A copy is made of the provided array.</item>
         /// </list>

test/OpenTelemetry.Tests/Metrics/MeterProviderTests.cs

@@ -0,0 +1,45 @@
+// <copyright file="MeterProviderTests.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// 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.
+// </copyright>
+
+using System.Collections.Generic;
+using OpenTelemetry.Exporter;
+using Xunit;
+
+namespace OpenTelemetry.Metrics.Tests
+{
+    public class MeterProviderTests
+    {
+        [Fact]
+        public void MeterProviderFindExporterTest()
+        {
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            Assert.True(meterProvider.TryFindExporter(out InMemoryExporter<Metric> inMemoryExporter));
+            Assert.False(meterProvider.TryFindExporter(out MyExporter myExporter));
+        }
+
+        private class MyExporter : BaseExporter<Metric>
+        {
+            public override ExportResult Export(in Batch<Metric> batch)
+            {
+                return ExportResult.Success;
+            }
+        }
+    }
+}