diff --git a/compiler/src/test/scala/org/capnproto/EncodingTest.scala b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
index ad7d0d9..8d09518 100644
--- a/compiler/src/test/scala/org/capnproto/EncodingTest.scala
+++ b/compiler/src/test/scala/org/capnproto/EncodingTest.scala
@@ -24,6 +24,15 @@ class EncodingSuite extends FunSuite {
     TestUtil.checkTestMessage(allTypes.asReader());
   }
 
+  test("Groups") {
+    val builder = new MessageBuilder();
+    val root = builder.initRoot(TestGroups.factory);
+
+    //val foo = root.getGroups().initFoo();
+
+  }
+
+
   // to debug, do this:
   //Serialize.writeMessage((new java.io.FileOutputStream("/Users/dwrensha/Desktop/test.dat")).getChannel(),
   //                       message);
diff --git a/compiler/src/test/schema/test.capnp b/compiler/src/test/schema/test.capnp
index 6819613..9bc95ef 100644
--- a/compiler/src/test/schema/test.capnp
+++ b/compiler/src/test/schema/test.capnp
@@ -59,4 +59,106 @@ struct TestOutOfOrder {
   grault @1 :Text;
   garply @7 :Text;
   waldo @5 :Text;
-}
\ No newline at end of file
+}
+
+
+struct TestUnion {
+  union0 @0! :union {
+    # Pack union 0 under ideal conditions: there is no unused padding space prior to it.
+    u0f0s0  @4: Void;
+    u0f0s1  @5: Bool;
+    u0f0s8  @6: Int8;
+    u0f0s16 @7: Int16;
+    u0f0s32 @8: Int32;
+    u0f0s64 @9: Int64;
+    u0f0sp  @10: Text;
+
+    # Pack more stuff into union0 -- should go in same space.
+    u0f1s0  @11: Void;
+    u0f1s1  @12: Bool;
+    u0f1s8  @13: Int8;
+    u0f1s16 @14: Int16;
+    u0f1s32 @15: Int32;
+    u0f1s64 @16: Int64;
+    u0f1sp  @17: Text;
+  }
+
+  # Pack one bit in order to make pathological situation for union1.
+  bit0 @18: Bool;
+
+  union1 @1! :union {
+    # Pack pathologically bad case.  Each field takes up new space.
+    u1f0s0  @19: Void;
+    u1f0s1  @20: Bool;
+    u1f1s1  @21: Bool;
+    u1f0s8  @22: Int8;
+    u1f1s8  @23: Int8;
+    u1f0s16 @24: Int16;
+    u1f1s16 @25: Int16;
+    u1f0s32 @26: Int32;
+    u1f1s32 @27: Int32;
+    u1f0s64 @28: Int64;
+    u1f1s64 @29: Int64;
+    u1f0sp  @30: Text;
+    u1f1sp  @31: Text;
+
+    # Pack more stuff into union1 -- each should go into the same space as corresponding u1f0s*.
+    u1f2s0  @32: Void;
+    u1f2s1  @33: Bool;
+    u1f2s8  @34: Int8;
+    u1f2s16 @35: Int16;
+    u1f2s32 @36: Int32;
+    u1f2s64 @37: Int64;
+    u1f2sp  @38: Text;
+  }
+
+  # Fill in the rest of that bitfield from earlier.
+  bit2 @39: Bool;
+  bit3 @40: Bool;
+  bit4 @41: Bool;
+  bit5 @42: Bool;
+  bit6 @43: Bool;
+  bit7 @44: Bool;
+
+  # Interleave two unions to be really annoying.
+  # Also declare in reverse order to make sure union discriminant values are sorted by field number
+  # and not by declaration order.
+  union2 @2! :union {
+    u2f0s64 @54: Int64;
+    u2f0s32 @52: Int32;
+    u2f0s16 @50: Int16;
+    u2f0s8 @47: Int8;
+    u2f0s1 @45: Bool;
+  }
+
+  union3 @3! :union {
+    u3f0s64 @55: Int64;
+    u3f0s32 @53: Int32;
+    u3f0s16 @51: Int16;
+    u3f0s8 @48: Int8;
+    u3f0s1 @46: Bool;
+  }
+
+  byte0 @49: UInt8;
+}
+
+
+struct TestGroups {
+  groups :union {
+    foo :group {
+      corge @0 :Int32;
+      grault @2 :Int64;
+      garply @8 :Text;
+    }
+    bar :group {
+      corge @3 :Int32;
+      grault @4 :Text;
+      garply @5 :Int64;
+    }
+    baz :group {
+      corge @1 :Int32;
+      grault @6 :Text;
+      garply @7 :Text;
+    }
+  }
+}