Add testcase for ChannelInitializer.initChannel(...) when throwing an Exception (#8188)

Motivation:

We had a report that the exception may not be correctly propagated. This test shows it is.

Modifications:

Add testcase.

Result:

Test for https://github.com/netty/netty/issues/8158

transport/src/test/java/io/netty/channel/ChannelInitializerTest.java

@@ -30,6 +30,7 @@ import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
@@ -63,6 +64,47 @@ public class ChannelInitializerTest {
         group.shutdownGracefully(0, TIMEOUT_MILLIS, TimeUnit.MILLISECONDS).syncUninterruptibly();
     }
 
+    @Test
+    public void testInitChannelThrowsRegisterFirst() {
+        testInitChannelThrows(true);
+    }
+
+    @Test
+    public void testInitChannelThrowsRegisterAfter() {
+        testInitChannelThrows(false);
+    }
+
+    private void testInitChannelThrows(boolean registerFirst) {
+        final Exception exception = new Exception();
+        final AtomicReference<Throwable> causeRef = new AtomicReference<Throwable>();
+
+        ChannelPipeline pipeline = new LocalChannel().pipeline();
+
+        if (registerFirst) {
+            group.register(pipeline.channel()).syncUninterruptibly();
+        }
+        pipeline.addFirst(new ChannelInitializer<Channel>() {
+            @Override
+            protected void initChannel(Channel ch) throws Exception {
+                throw exception;
+            }
+
+            @Override
+            public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
+                causeRef.set(cause);
+                super.exceptionCaught(ctx, cause);
+            }
+        });
+
+        if (!registerFirst) {
+            group.register(pipeline.channel()).syncUninterruptibly();
+        }
+        pipeline.channel().close().syncUninterruptibly();
+        pipeline.channel().closeFuture().syncUninterruptibly();
+
+        assertSame(exception, causeRef.get());
+    }
+
     @Test
     public void testChannelInitializerInInitializerCorrectOrdering() {
         final ChannelInboundHandlerAdapter handler1 = new ChannelInboundHandlerAdapter();