add doc and test for AddCommentForIssue method

src/YouTrackSharp/Issues/IIssuesService.cs

@@ -146,6 +146,16 @@ Task<ICollection<Issue>> GetIssues(string filter = null, int? skip = null, int?
         /// <exception cref="T:System.Net.HttpRequestException">When the call to the remote YouTrack server instance failed.</exception>
         Task<IEnumerable<Comment>> GetCommentsForIssue(string issueId, bool wikifyDescription = false);
 
+        /// <summary>
+        /// Adds a comment for an issue on the server.
+        /// </summary>
+        /// <remarks>Uses the REST API <a href="https://www.jetbrains.com/help/youtrack/devportal/resource-api-issues-issueID-comments.html#create-IssueComment-method">Update a Comment</a>.</remarks>
+        /// <param name="issueId">Id of the issue to add comment to.</param>
+        /// <param name="text">The text of the new comment.</param>
+        /// <exception cref="T:System.ArgumentNullException">When the <paramref name="issueId"/> or <paramref name="text"/> is null or empty.</exception>
+        /// <exception cref="T:System.Net.HttpRequestException">When the call to the remote YouTrack server instance failed.</exception>
+        Task AddCommentForIssue(string issueId, string text);
+
         /// <summary>
         /// Updates a comment for an issue on the server.
         /// </summary>

tests/YouTrackSharp.Tests/Integration/Issues/Comments/AddCommentForIssue.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Xunit;
+using YouTrackSharp.Tests.Infrastructure;
+
+// ReSharper disable once CheckNamespace
+namespace YouTrackSharp.Tests.Integration.Issues
+{
+    public partial class IssuesServiceTests
+    {
+        public class AddCommentForIssue
+        {
+            [Fact]
+            public async Task Valid_Connection_Adds_Comment_For_Issue()
+            {
+                // Arrange
+                var connection = Connections.Demo1Token;
+                using (var temporaryIssueContext = await TemporaryIssueContext.Create(connection, GetType()))
+                {
+                    var service = connection.CreateIssuesService();
+                    var commentText = "Test comment " + DateTime.UtcNow.ToString("U");
+
+                    // Act
+                    await service.AddCommentForIssue(temporaryIssueContext.Issue.Id, commentText);
+
+                    // Assert
+                    var comments = await service.GetCommentsForIssue(temporaryIssueContext.Issue.Id);
+
+                    Assert.NotNull(comments.FirstOrDefault(comment => comment.Text.Equals(commentText)));
+
+                    await temporaryIssueContext.Destroy();
+                }
+            }
+        }
+    }
+}