Foo foo = new Foo();
ValueStack vs = ActionContext.getContext().getValueStack();
vs.getContext().put(XWorkConverter.REPORT_CONVERSION_ERRORS, Boolean.TRUE);
XWorkConverter c = (XWorkConverter)((OgnlTypeConverterWrapper) Ognl.getTypeConverter(vs.getContext())).getTarget();
c.registerConverter(Cat.class.getName(), new FooBarConverter());
vs.push(foo);
vs.setValue("cats", new String[]{"1", "2"});
assertNotNull(foo.getCats());
assertEquals(2, foo.getCats().size());