public void testUnionSupertype() throws FusionException {
FreeVars vars1 = new FreeVars();
vars1 = vars1.addVar(new SpecVar("foo"), "SnaFu");
FreeVars vars2 = new FreeVars();
vars2 = vars2.addVar(new SpecVar("foo"), "Foo");
vars2 = vars2.addVar(new SpecVar("bar"), "Bar");
vars2 = vars2.union(vars1);
assertEquals(2, vars2.size());
assertEquals("Foo", vars2.getType(new SpecVar("foo")));
assertEquals("Bar", vars2.getType(new SpecVar("bar")));