@Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (Map.Entry<ConfigKey<?>, ConfigInstance.Builder> entry : configs.entrySet()) {
            sb.append(entry.getKey()).append("=>").append(entry.getValue());
        }
        return sb.toString();
    }
@Test
    public void testToString() {
        ConfigSet set = new ConfigSet();
        SimpletypesConfig.Builder builder = new SimpletypesConfig.Builder();
        set.addBuilder("foo", builder);
        assertTrue(Pattern.matches("name=foo.simpletypes,configId=foo=>com.yahoo.foo.SimpletypesConfig.*",
                set.toString()));
    }