diff --git a/src/test/scala/tlschannel/NettySslEngineTest.java b/src/test/scala/tlschannel/NettySslEngineTest.java
new file mode 100644
index 00000000..8c742311
--- /dev/null
+++ b/src/test/scala/tlschannel/NettySslEngineTest.java
@@ -0,0 +1,99 @@
+package tlschannel;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.handler.ssl.SslContextBuilder;
+import io.netty.handler.ssl.SslProvider;
+import io.netty.handler.ssl.util.SimpleTrustManagerFactory;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.nio.channels.ByteChannel;
+import java.security.KeyStore;
+import java.security.cert.X509Certificate;
+import javax.net.ssl.*;
+import javax.net.ssl.ManagerFactoryParameters;
+import javax.net.ssl.SSLEngine;
+import javax.net.ssl.TrustManager;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.TestInstance.Lifecycle;
+
+@TestInstance(Lifecycle.PER_CLASS)
+public class NettySslEngineTest {
+
+    // dummy handshake as minimal sanity test
+    @Test
+    void testDummyHandshake() throws SSLException {
+        io.netty.handler.ssl.SslContext ctx = SslContextBuilder.forClient()
+                .sslProvider(SslProvider.OPENSSL)
+                .trustManager(dummyTrustManagerFactory)
+                .protocols("TLSv1.3")
+                .build();
+        SSLEngine sslEngine = ctx.newEngine(ByteBufAllocator.DEFAULT, "test", 0);
+
+        ClientTlsChannel channel = ClientTlsChannel.newBuilder(new DummyByteChannel(), sslEngine)
+                .withEncryptedBufferAllocator(new HeapBufferAllocator())
+                .build();
+
+        assertThrows(NeedsWriteException.class, () -> channel.handshake());
+    }
+
+    private final TrustManagerFactory dummyTrustManagerFactory = new SimpleTrustManagerFactory() {
+        @Override
+        public void engineInit(KeyStore keyStore) {}
+
+        @Override
+        public void engineInit(ManagerFactoryParameters params) {}
+
+        @Override
+        public TrustManager[] engineGetTrustManagers() {
+            return new TrustManager[] {new DummyTrustManager()};
+        }
+    };
+
+    private static class DummyByteChannel implements ByteChannel {
+        @Override
+        public boolean isOpen() {
+            return false;
+        }
+
+        @Override
+        public void close() {}
+
+        @Override
+        public int write(ByteBuffer src) {
+            return 0;
+        }
+
+        @Override
+        public int read(ByteBuffer dst) {
+            return 0;
+        }
+    }
+
+    private static class DummyTrustManager extends X509ExtendedTrustManager {
+        @Override
+        public void checkClientTrusted(X509Certificate[] certs, String s) {}
+
+        @Override
+        public void checkServerTrusted(X509Certificate[] certs, String s) {}
+
+        @Override
+        public X509Certificate[] getAcceptedIssuers() {
+            return new X509Certificate[0];
+        }
+
+        @Override
+        public void checkClientTrusted(X509Certificate[] certs, String s, Socket socket) {}
+
+        @Override
+        public void checkServerTrusted(X509Certificate[] certs, String s, Socket socket) {}
+
+        @Override
+        public void checkClientTrusted(X509Certificate[] certs, String s, SSLEngine sslEngine) {}
+
+        @Override
+        public void checkServerTrusted(X509Certificate[] certs, String s, SSLEngine sslEngine) {}
+    }
+}
diff --git a/src/test/scala/tlschannel/NettySslEngineTest.scala b/src/test/scala/tlschannel/NettySslEngineTest.scala
deleted file mode 100644
index e73a509a..00000000
--- a/src/test/scala/tlschannel/NettySslEngineTest.scala
+++ /dev/null
@@ -1,69 +0,0 @@
-package tlschannel
-
-import io.netty.buffer.ByteBufAllocator
-import io.netty.handler.ssl.SslContextBuilder
-import io.netty.handler.ssl.SslProvider
-import io.netty.handler.ssl.util.SimpleTrustManagerFactory
-import org.junit.jupiter.api.{Test, TestInstance}
-import org.junit.jupiter.api.TestInstance.Lifecycle
-import org.junit.jupiter.api.Assertions.assertThrows
-
-import javax.net.ssl.{ManagerFactoryParameters, SSLEngine, TrustManager, TrustManagerFactory, X509ExtendedTrustManager}
-import java.net.Socket
-import java.nio.ByteBuffer
-import java.nio.channels.ByteChannel
-import java.security.KeyStore
-import java.security.cert.X509Certificate
-
-@TestInstance(Lifecycle.PER_CLASS)
-class NettySslEngineTest {
-
-  import NettySslEngineTest._
-
-  // dummy handshake as minimal sanity test
-  @Test
-  def testDummyHandshake(): Unit = {
-    val ctx = SslContextBuilder
-      .forClient()
-      .sslProvider(SslProvider.OPENSSL)
-      .trustManager(dummyTrustManagerFactory)
-      .protocols("TLSv1.3")
-      .build()
-    val sslEngine = ctx.newEngine(ByteBufAllocator.DEFAULT, "test", 0)
-
-    val channel = ClientTlsChannel
-      .newBuilder(new DummyByteChannel(), sslEngine)
-      .withEncryptedBufferAllocator(new HeapBufferAllocator())
-      .build()
-
-    assertThrows(classOf[NeedsWriteException], () => channel.handshake())
-  }
-
-}
-
-object NettySslEngineTest {
-
-  private val dummyTrustManagerFactory: TrustManagerFactory = new SimpleTrustManagerFactory() {
-    private val trustManagers = Array[TrustManager](new DummyTrustManager())
-    override def engineInit(keyStore: KeyStore): Unit = {}
-    override def engineInit(params: ManagerFactoryParameters): Unit = {}
-    override def engineGetTrustManagers(): Array[TrustManager] = trustManagers
-  }
-
-  private class DummyByteChannel extends ByteChannel {
-    override def isOpen = false
-    override def close(): Unit = {}
-    override def write(src: ByteBuffer) = 0
-    override def read(dst: ByteBuffer) = 0
-  }
-
-  private class DummyTrustManager extends X509ExtendedTrustManager {
-    override def checkClientTrusted(certs: Array[X509Certificate], s: String): Unit = {}
-    override def checkServerTrusted(certs: Array[X509Certificate], s: String): Unit = {}
-    override def getAcceptedIssuers: Array[X509Certificate] = Array[X509Certificate]()
-    override def checkClientTrusted(certs: Array[X509Certificate], s: String, socket: Socket): Unit = {}
-    override def checkServerTrusted(certs: Array[X509Certificate], s: String, socket: Socket): Unit = {}
-    override def checkClientTrusted(certs: Array[X509Certificate], s: String, sslEngine: SSLEngine): Unit = {}
-    override def checkServerTrusted(certs: Array[X509Certificate], s: String, sslEngine: SSLEngine): Unit = {}
-  }
-}