Use assertThat#instanceOf and assertThat#isNotInstanceOf [Codec-H…

…TTP] (netty#13135)

Motivation:
We use `assertTrue(obj instanceOf Cat)` for asserting object instances. While this is correct and works, it becomes impossible to debug when the assertion fails because we have no clue at all which instance type made the assertion fail.

Modification:
To address this, we should use `assertThat#instanceOf` which will do the exact same thing but in a much cleaner way. Also, it will give us more information when it fails like why the assertion of instance check failed and what exactly we got in place of the expected one.

Result:
Cleaner and easier to debug test case failure

This PR migrates the entire Codec-HTTP module completely to the new API.

codec-http/src/test/java/io/netty/handler/codec/http/HttpClientCodecTest.java

@@ -380,7 +380,7 @@ public void testInformationalResponseKeepsPairsInSync() {
         HttpContent content = ch.readInbound();
         // HTTP 102 is not allowed to have content.
         assertThat(content.content().readableBytes(), is(0));
-        assertThat(content, CoreMatchers.<HttpContent>instanceOf(LastHttpContent.class));
+        assertThat(content, instanceOf(LastHttpContent.class));
         content.release();
 
         assertTrue(ch.writeOutbound(new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/")));
@@ -395,7 +395,7 @@ public void testInformationalResponseKeepsPairsInSync() {
         content = ch.readInbound();
         // HTTP 200 has content.
         assertThat(content.content().readableBytes(), is(8));
-        assertThat(content, CoreMatchers.<HttpContent>instanceOf(LastHttpContent.class));
+        assertThat(content, instanceOf(LastHttpContent.class));
         content.release();
 
         assertThat(ch.finish(), is(false));

codec-http/src/test/java/io/netty/handler/codec/http/HttpRequestDecoderTest.java

@@ -20,6 +20,7 @@
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.util.AsciiString;
 import io.netty.util.CharsetUtil;
+import org.hamcrest.CoreMatchers;
 import org.junit.jupiter.api.Test;
 
 import java.util.ArrayList;
@@ -307,7 +308,7 @@ public void testTooLargeInitialLine() {
         assertTrue(channel.writeInbound(Unpooled.copiedBuffer(requestStr, CharsetUtil.US_ASCII)));
         HttpRequest request = channel.readInbound();
         assertTrue(request.decoderResult().isFailure());
-        assertTrue(request.decoderResult().cause() instanceof TooLongHttpLineException);
+        assertThat(request.decoderResult().cause(), instanceOf(TooLongHttpLineException.class));
         assertFalse(channel.finish());
     }
 

codec-http/src/test/java/io/netty/handler/codec/http/HttpServerUpgradeHandlerTest.java

@@ -34,6 +34,7 @@
 import io.netty.util.ReferenceCountUtil;
 import org.junit.jupiter.api.Test;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
@@ -179,7 +180,7 @@ protected boolean shouldHandleUpgradeRequest(HttpRequest req) {
         assertNull(channel.pipeline().get("marker"));
 
         HttpRequest req = channel.readInbound();
-        assertFalse(req instanceof FullHttpRequest); // Should not be aggregated.
+        assertThat(req).isNotInstanceOf(FullHttpRequest.class); // Should not be aggregated.
         assertTrue(req.headers().contains(HttpHeaderNames.CONNECTION, "Upgrade", false));
         assertTrue(req.headers().contains(HttpHeaderNames.UPGRADE, "do-not-upgrade", false));
         assertTrue(channel.readInbound() instanceof LastHttpContent);

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketServerHandshaker13Test.java

@@ -40,6 +40,7 @@
 import java.util.Iterator;
 
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
+import static org.hamcrest.CoreMatchers.instanceOf;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -188,7 +189,7 @@ private static void testCloseReason0(ChannelHandler... handlers) {
             // expected
         }
         ReferenceCounted closeMessage = ch.readOutbound();
-        assertThat(closeMessage, CoreMatchers.instanceOf(ByteBuf.class));
+        assertThat(closeMessage, instanceOf(ByteBuf.class));
         closeMessage.release();
         assertFalse(ch.finish());
     }