add Unions test

compiler/src/test/scala/org/capnproto/EncodingSuite.scala

@@ -230,6 +230,17 @@ class EncodingSuite extends FunSuite {
     TestUtil.checkSettedDefaultMessage(defaults.asReader())
   }
 
+  test("Unions") {
+    val builder = new MessageBuilder()
+    val root = builder.initRoot(TestUnion.factory)
+    val u0 = root.initUnion0()
+    u0.initU0f1sp(10)
+    assert(u0.which() == TestUnion.Union0.Which.U0F1SP)
+
+    u0.initPrimitiveList(10)
+    assert(u0.which() == TestUnion.Union0.Which.PRIMITIVE_LIST)
+  }
+
   test("Groups") {
     val builder = new MessageBuilder()
     val root = builder.initRoot(TestGroups.factory)

compiler/src/test/schema/test.capnp

@@ -180,6 +180,8 @@ struct TestUnion {
     u0f1s32 @15: Int32;
     u0f1s64 @16: Int64;
     u0f1sp  @17: Text;
+
+    primitiveList @56: List(UInt32);
   }
 
   # Pack one bit in order to make pathological situation for union1.
@@ -393,6 +395,14 @@ struct GenericMap(K, V)
  c @3 :List(List(List(Entry)));
 }
 
+# TODO. this is currently broken
+#struct TestGenericUnion(T) {
+#  union0: union {
+#    nothing @0 :Void;
+#    something @1 :T;
+#  }
+#}
+
 struct TestEmptyStruct {}
 
 struct TestConstants {