diff --git a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpCommandTest.java b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpCommandTest.java
index 3458a78e9d..c53b9d1158 100644
--- a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpCommandTest.java
+++ b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpCommandTest.java
@@ -15,9 +15,13 @@
  */
 package io.netty.handler.codec.smtp;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class SmtpCommandTest {
     @Test
diff --git a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpRequestEncoderTest.java b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpRequestEncoderTest.java
index dab4dd5309..7c9e056fbc 100644
--- a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpRequestEncoderTest.java
+++ b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpRequestEncoderTest.java
@@ -20,11 +20,13 @@ import io.netty.buffer.Unpooled;
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.handler.codec.EncoderException;
 import io.netty.util.CharsetUtil;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class SmtpRequestEncoderTest {
 
@@ -106,12 +108,17 @@ public class SmtpRequestEncoderTest {
         assertEquals("DATA\r\nSubject: Test\r\n\r\nTest\r\n.\r\n", getWrittenString(channel));
     }
 
-    @Test(expected = EncoderException.class)
+    @Test
     public void testThrowsIfContentExpected() {
-        EmbeddedChannel channel = new EmbeddedChannel(new SmtpRequestEncoder());
+        final EmbeddedChannel channel = new EmbeddedChannel(new SmtpRequestEncoder());
         try {
             assertTrue(channel.writeOutbound(SmtpRequests.data()));
-            channel.writeOutbound(SmtpRequests.noop());
+            assertThrows(EncoderException.class, new Executable() {
+                @Override
+                public void execute() {
+                    channel.writeOutbound(SmtpRequests.noop());
+                }
+            });
         } finally {
             channel.finishAndReleaseAll();
         }
diff --git a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
index 50846d8de0..5f5918d57c 100644
--- a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
+++ b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
@@ -20,11 +20,16 @@ import io.netty.buffer.Unpooled;
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.handler.codec.DecoderException;
 import io.netty.util.CharsetUtil;
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
 
 import java.util.List;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 public class SmtpResponseDecoderTest {
 
@@ -106,22 +111,37 @@ public class SmtpResponseDecoderTest {
         assertNull(channel.readInbound());
     }
 
-    @Test(expected = DecoderException.class)
+    @Test
     public void testDecodeInvalidSeparator() {
-        EmbeddedChannel channel = newChannel();
-        assertTrue(channel.writeInbound(newBuffer("200:Ok\r\n")));
+        final EmbeddedChannel channel = newChannel();
+        assertThrows(DecoderException.class, new Executable() {
+            @Override
+            public void execute() {
+                channel.writeInbound(newBuffer("200:Ok\r\n"));
+            }
+        });
     }
 
-    @Test(expected = DecoderException.class)
+    @Test
     public void testDecodeInvalidCode() {
-        EmbeddedChannel channel = newChannel();
-        assertTrue(channel.writeInbound(newBuffer("xyz Ok\r\n")));
+        final EmbeddedChannel channel = newChannel();
+        assertThrows(DecoderException.class, new Executable() {
+            @Override
+            public void execute() {
+                channel.writeInbound(newBuffer("xyz Ok\r\n"));
+            }
+        });
     }
 
-    @Test(expected = DecoderException.class)
+    @Test
     public void testDecodeInvalidLine() {
-        EmbeddedChannel channel = newChannel();
-        assertTrue(channel.writeInbound(newBuffer("Ok\r\n")));
+        final EmbeddedChannel channel = newChannel();
+        assertThrows(DecoderException.class, new Executable() {
+            @Override
+            public void execute() {
+                channel.writeInbound(newBuffer("Ok\r\n"));
+            }
+        });
     }
 
     private static EmbeddedChannel newChannel() {