public static CredentialService getInstance() {
        return getInstance(null);
    }
@Test
    void testGetInstance3() throws NoSuchFieldException, IllegalAccessException {
        System.setProperty(IdentifyConstants.PROJECT_NAME_PROPERTY, APP_NAME);
        CredentialService credentialService1 = CredentialService.getInstance();
        Field appNameField = credentialService1.getClass().getDeclaredField("appName");
        appNameField.setAccessible(true);
        String appName = (String) appNameField.get(credentialService1);
        assertEquals(APP_NAME, appName);
    }