diff --git a/core/src/test/java/io/grpc/internal/ForwardingReadableBufferTest.java b/core/src/test/java/io/grpc/internal/ForwardingReadableBufferTest.java
index b778f25e5de..029a406b1f5 100644
--- a/core/src/test/java/io/grpc/internal/ForwardingReadableBufferTest.java
+++ b/core/src/test/java/io/grpc/internal/ForwardingReadableBufferTest.java
@@ -17,13 +17,12 @@
 package io.grpc.internal;
 
 import static org.junit.Assert.assertEquals;
-import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import io.grpc.ForwardingTestUtil;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.io.OutputStream;
 import java.lang.reflect.Method;
 import java.nio.ByteBuffer;
 import java.util.Collections;
@@ -36,13 +35,10 @@
 import org.mockito.junit.MockitoJUnit;
 import org.mockito.junit.MockitoRule;
 
-/**
- * Tests for {@link ForwardingReadableBuffer}.
- */
+/** Tests for {@link ForwardingReadableBuffer}. */
 @RunWith(JUnit4.class)
 public class ForwardingReadableBufferTest {
-  @Rule
-  public final MockitoRule mocks = MockitoJUnit.rule();
+  @Rule public final MockitoRule mocks = MockitoJUnit.rule();
 
   @Mock private ReadableBuffer delegate;
   private ForwardingReadableBuffer buffer;
@@ -55,10 +51,7 @@ public void setUp() {
   @Test
   public void allMethodsForwarded() throws Exception {
     ForwardingTestUtil.testMethodsForwarded(
-        ReadableBuffer.class,
-        delegate,
-        buffer,
-        Collections.<Method>emptyList());
+        ReadableBuffer.class, delegate, buffer, Collections.<Method>emptyList());
   }
 
   @Test
@@ -99,7 +92,7 @@ public void readBytes() {
 
   @Test
   public void readBytes_overload1() {
-    ByteBuffer dest = mock(ByteBuffer.class);
+    ByteBuffer dest = ByteBuffer.allocate(0);
     buffer.readBytes(dest);
 
     verify(delegate).readBytes(dest);
@@ -107,7 +100,7 @@ public void readBytes_overload1() {
 
   @Test
   public void readBytes_overload2() throws IOException {
-    OutputStream dest = mock(OutputStream.class);
+    OutputStream dest = new ByteArrayOutputStream();
     buffer.readBytes(dest, 1);
 
     verify(delegate).readBytes(dest, 1);