public String assignNewDataSourceName() {
        return null == defaultDataSource ? new ArrayList<>(dataSourceNames).get(ThreadLocalRandom.current().nextInt(dataSourceNames.size())) : defaultDataSource;
    }
@Test
    void assertAssignNewDataSourceName() {
        SingleRuleConfiguration singleRuleConfig = new SingleRuleConfiguration();
        singleRuleConfig.setDefaultDataSource("foo_ds");
        SingleRule singleRule = new SingleRule(
                singleRuleConfig, DefaultDatabase.LOGIC_NAME, new H2DatabaseType(), dataSourceMap, Collections.singleton(mock(ShardingSphereRule.class, RETURNS_DEEP_STUBS)));
        assertThat(singleRule.assignNewDataSourceName(), is("foo_ds"));
    }