protected void createRealm(String testMethodName) {
        JdbcRealm realm = (JdbcRealm) securityManager.getRealms().iterator().next();
        realmMap.put(testMethodName, realm);
    }
Creates a realm for a test method and puts it in the realMap.
core/src/test/java/org/apache/shiro/realm/jdbc/JDBCRealmTest.java