public Array getArray(String name) {
        Array a = arrayMap.get(name);
        if (a == null) {
            validateArray(name);
            a = new Array(configDefinition, name);
            arrayMap.put(name, a);
        }
        return a;
    }
@Test(expected=IllegalArgumentException.class)
    public void require_that_arrays_must_exist() {
        builderWithDef.getArray("arraydoesnotexist");
    }