public <T extends ShardingSphereRule> T getSingleRule(final Class<T> clazz) {
        Collection<T> foundRules = findRules(clazz);
        Preconditions.checkState(1 == foundRules.size(), "Rule `%s` should have and only have one instance.", clazz.getSimpleName());
        return foundRules.iterator().next();
    }
@Test
    void assertGetSingleRule() {
        assertThat(ruleMetaData.getSingleRule(ShardingSphereRuleFixture.class), instanceOf(ShardingSphereRuleFixture.class));
    }