public String getSecurityCredentialsUrl() {
        if (securityCredentialsUrl == null && ramRoleName != null) {
            return RAM_SECURITY_CREDENTIALS_URL + ramRoleName;
        }
        return securityCredentialsUrl;
    }
@Test
    void testGetSecurityCredentialsUrl() {
        assertNull(StsConfig.getInstance().getSecurityCredentialsUrl());
        String expect = "localhost";
        StsConfig.getInstance().setSecurityCredentialsUrl(expect);
        assertEquals(expect, StsConfig.getInstance().getSecurityCredentialsUrl());
    }