diff --git a/oncrpc4j-core/src/test/java/org/dcache/oncrpc4j/xdr/XdrOpaqueTest.java b/oncrpc4j-core/src/test/java/org/dcache/oncrpc4j/xdr/XdrOpaqueTest.java
new file mode 100644
index 00000000..652fa88a
--- /dev/null
+++ b/oncrpc4j-core/src/test/java/org/dcache/oncrpc4j/xdr/XdrOpaqueTest.java
@@ -0,0 +1,128 @@
+package org.dcache.oncrpc4j.xdr;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class XdrOpaqueTest {
+
+    @Test
+    public void testEncode() throws IOException {
+
+        XdrOpaque opaque = new XdrOpaque("some bytes".getBytes(StandardCharsets.UTF_8));
+
+        try(Xdr xdr = new Xdr(128)) {
+
+            xdr.beginEncoding();
+            opaque.xdrEncode(xdr);
+            xdr.endEncoding();
+
+            xdr.beginDecoding();
+
+            assertArrayEquals("invalid opaque value", opaque.getOpaque(), xdr.xdrDecodeDynamicOpaque());
+        }
+    }
+
+    @Test
+    public void testDecode() throws IOException {
+
+        byte[] value = "some bytes".getBytes(StandardCharsets.UTF_8);
+
+        try (Xdr xdr = new Xdr(128)) {
+
+            xdr.beginEncoding();
+            xdr.xdrEncodeDynamicOpaque(value);
+            xdr.endEncoding();
+
+            xdr.beginDecoding();
+
+            XdrOpaque opaque = new XdrOpaque(xdr);
+
+            assertArrayEquals("invalid opaque value", value, opaque.getOpaque());
+        }
+    }
+
+    @Test
+    public void testSameMustBeEqual() throws IOException {
+
+        XdrOpaque opaque = new XdrOpaque("some bytes".getBytes(StandardCharsets.UTF_8));
+
+        assertTrue("opaques with equal values must be equal", opaque.equals(opaque));
+    }
+
+    @Test
+    public void testEqualsByValue() throws IOException {
+
+        XdrOpaque opaque1 = new XdrOpaque("some bytes".getBytes(StandardCharsets.UTF_8));
+        XdrOpaque opaque2 = new XdrOpaque("some bytes".getBytes(StandardCharsets.UTF_8));
+
+        assertTrue("opaques with equal values must be equal", opaque1.equals(opaque2));
+        assertTrue("equal objects must have the same hashcode", opaque1.hashCode() == opaque2.hashCode());
+    }
+
+    @Test
+    public void testDifferentTypesCantBeEqual() throws IOException {
+
+        byte[] data = "some bytes".getBytes(StandardCharsets.UTF_8);
+        XdrOpaque opaque = new XdrOpaque(data);
+
+        assertFalse("opaques with equal values must be equal", opaque.equals(data));
+    }
+
+
+    @Test
+    public void testDifferentObjectDifferentStrings() {
+        XdrOpaque opaque1 = new XdrOpaque("some bytes".getBytes(StandardCharsets.UTF_8));
+        XdrOpaque opaque2 = new XdrOpaque("some other bytes".getBytes(StandardCharsets.UTF_8));
+        assertNotNull("toString should not return null", opaque1.toString());
+        assertNotNull("toString should not return null", opaque2.toString());
+
+        assertNotEquals("different by value must return different strings",
+                opaque1.toString(), opaque2.toString());
+    }
+
+    @Test
+    public void testDecodeWellKnown() throws IOException {
+
+        byte[] data = new byte[]{
+            0x0, 0x0, 0x0, 0x08, // size
+            0x0C, 0x0A, 0x0F, 0x0E, 0x0B, 0x0A, 0x0B, 0x0E // data
+        };
+
+        try (Xdr xdr = new Xdr(data)) {
+            xdr.beginDecoding();
+
+            XdrOpaque opaque = new XdrOpaque(xdr);
+            // the data part must match (e.g without size)
+            assertArrayEquals(Arrays.copyOfRange(data, 4, 12), opaque.getOpaque());
+        }
+    }
+
+    @Test
+    public void testEncodeWellKnown() throws IOException {
+
+        byte[] data = new byte[]{
+            0x0C, 0x0A, 0x0F, 0x0E, 0x0B, 0x0A, 0x0B, 0x0E // data
+        };
+
+        byte[] expected = new byte[]{
+            0x0, 0x0, 0x0, 0x08, // size
+            0x0C, 0x0A, 0x0F, 0x0E, 0x0B, 0x0A, 0x0B, 0x0E // data
+        };
+
+        try (Xdr xdr = new Xdr(16)) {
+            xdr.beginEncoding();
+
+            XdrOpaque opaque = new XdrOpaque(data);
+            opaque.xdrEncode(xdr);
+
+            xdr.endEncoding();
+
+            // the data part must match (e.g without size)
+            assertArrayEquals(expected, xdr.getBytes());
+        }
+    }
+
+}