Add trailers test

src/Servers/Kestrel/test/InMemory.FunctionalTests/Http2/Http2StreamTests.cs

@@ -2213,6 +2213,44 @@ await ExpectAsync(Http2FrameType.DATA,
             Assert.Equal("200", _decodedHeaders[HeaderNames.Status]);
         }
 
+        [Fact]
+        public async Task ResponseTrailers_WithNonAsciiAndCustomEncoder_Works()
+        {
+            // TODO: How to correctly modify this per test?
+            _serviceContext.ServerOptions.ResponseHeaderEncodingSelector = _ => Encoding.UTF8;
+
+            await InitializeConnectionAsync(async context =>
+            {
+                await context.Response.WriteAsync("Hello World");
+                context.Response.AppendTrailer("CustomName", "Custom 你好 Value");
+            });
+
+            await StartStreamAsync(1, _browserRequestHeaders, endStream: true);
+
+            var headersFrame = await ExpectAsync(Http2FrameType.HEADERS,
+                withLength: 32,
+                withFlags: (byte)Http2HeadersFrameFlags.END_HEADERS,
+                withStreamId: 1);
+
+            await ExpectAsync(Http2FrameType.DATA,
+                withLength: 11,
+                withFlags: (byte)Http2DataFrameFlags.NONE,
+                withStreamId: 1);
+
+            await ExpectAsync(Http2FrameType.DATA,
+                withLength: 0,
+                withFlags: (byte)Http2DataFrameFlags.END_STREAM,
+                withStreamId: 1);
+
+            await StopConnectionAsync(expectedLastStreamId: 1, ignoreNonGoAwayFrames: false);
+
+            _hpackDecoder.Decode(headersFrame.PayloadSequence, endHeaders: true, handler: this);
+
+            Assert.Equal(2, _decodedHeaders.Count);
+            Assert.Contains("date", _decodedHeaders.Keys, StringComparer.OrdinalIgnoreCase);
+            Assert.Equal("200", _decodedHeaders[HeaderNames.Status]);
+        }
+
         [Fact]
         public async Task ResponseTrailers_TooLong_Throws()
         {