Add FtpControlStream edge case unit tests; fix Span read path heap allocation

tests/CoreFtp.Tests.Integration/FtpControlStreamTests/When_reading_control_stream.cs

@@ -0,0 +1,131 @@
+namespace CoreFtp.Tests.Integration.FtpControlStreamTests
+{
+    using System;
+    using System.IO;
+    using System.Text;
+    using System.Threading;
+    using FluentAssertions;
+    using Infrastructure.Stream;
+    using Xunit;
+
+    public class When_reading_control_stream
+    {
+        private sealed class TestStream : FtpControlStream
+        {
+            public TestStream() : base( new FtpClientConfiguration(), null ) { }
+
+            public void SetBaseStream( Stream stream )
+            {
+                BaseStream = stream;
+            }
+
+            public string TestReadLine( Encoding encoding, CancellationToken token = default( CancellationToken ) )
+                => ReadLine( encoding, token );
+        }
+
+        private static MemoryStream ToStream( string content, Encoding encoding = null )
+        {
+            return new MemoryStream( ( encoding ?? Encoding.ASCII ).GetBytes( content ) );
+        }
+
+        [ Fact ]
+        public void ReadLine_returns_null_when_stream_is_empty()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( new MemoryStream() );
+
+            var result = sut.TestReadLine( Encoding.ASCII );
+
+            result.Should().BeNull();
+        }
+
+        [ Fact ]
+        public void ReadLine_returns_line_content_when_terminated_by_lf()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( ToStream( "220 Welcome\n" ) );
+
+            var result = sut.TestReadLine( Encoding.ASCII );
+
+            result.Should().Be( "220 Welcome" );
+        }
+
+        [ Fact ]
+        public void ReadLine_strips_cr_from_crlf_line_ending()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( ToStream( "220 Welcome\r\n" ) );
+
+            var result = sut.TestReadLine( Encoding.ASCII );
+
+            result.Should().Be( "220 Welcome" );
+        }
+
+        [ Fact ]
+        public void ReadLine_returns_null_for_incomplete_line_without_lf()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( ToStream( "220 Welcome" ) );
+
+            var result = sut.TestReadLine( Encoding.ASCII );
+
+            result.Should().BeNull();
+        }
+
+        [ Fact ]
+        public void ReadLine_throws_when_encoding_is_null()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( new MemoryStream() );
+
+            Action act = () => sut.TestReadLine( null );
+
+            act.ShouldThrow<ArgumentNullException>();
+        }
+
+        [ Fact ]
+        public void ReadLine_throws_when_cancellation_already_requested()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( ToStream( "220 Welcome\n" ) );
+            var cts = new CancellationTokenSource();
+            cts.Cancel();
+
+            Action act = () => sut.TestReadLine( Encoding.ASCII, cts.Token );
+
+            act.ShouldThrow<OperationCanceledException>();
+        }
+
+        [ Fact ]
+        public void ReadByte_returns_minus_one_when_network_stream_is_null()
+        {
+            var sut = new TestStream();
+
+            var result = sut.ReadByte();
+
+            result.Should().Be( -1 );
+        }
+
+        [ Fact ]
+        public void ReadByte_returns_byte_value_when_data_available()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( ToStream( "A" ) );
+
+            var result = sut.ReadByte();
+
+            result.Should().Be( (int) 'A' );
+        }
+
+        [ Fact ]
+        public void ReadByte_returns_minus_one_at_end_of_stream()
+        {
+            var sut = new TestStream();
+            sut.SetBaseStream( new MemoryStream() );
+
+            var result = sut.ReadByte();
+
+            result.Should().Be( -1 );
+        }
+    }
+}