如何测试main方法

今天的component有个commandline class需要测试main函数的返回值，我们知道正常情况下是无法测试commandline的类的，因为    public static final void main(String[] args) {}结束的时

候会调用system.exit(status).当然也会终止测试的jvm。也就是说如果我们直接这样写： public void testStatus(){     CommandLineClass.main(args)； } 这是行不通的，一是你无法获得返回值，而是后边的语句和测试全部会被强行终止。当然任何难题都有解决的办法，我们知道main函数返回的系统调用exit，会经过securityManage的检查是否拥有权限。所以我们可以实现自己的securitymanager并覆写 checkExit(int status) 方法，保存status状态，这样就搞定了。简单吧？ 这个是我刚才写的SecurityManager:

 /**

     * the mock security manager use for retrieve the exit status of the main method.

     * <p>

     * since the main method will call System.exit, we cannot make it executable with other tests because JVM

     * will be halt once main() method is called. so we can "stop" and "ignore" the exit call execute.

     * </p>

     * @author  netsafe

     */

    class MockSecurityManager extends SecurityManager {

        /**

         * the status value of the exit method.

         */

        private int status;



        /**

         * Throws a <code>SecurityException</code> if the calling thread is not allowed to cause the Java

         * Virtual Machine to halt with the specified status code.

         * <p>for this mock method,the SecurityException will always be thrown</p>

         * @param status

         *            the exit status.

         * @exception SecurityException

         *                if the calling thread does not have permission to halt the Java Virtual Machine with

         *                the specified status.

         */

        @Override

        public void checkExit(int status) {

            this.status = status;

            throw new SecurityException();

        }



        /**

         * return the exit status.

         * @return the exit status.

         */

        public int getStatus() {

            return status;

        }



        /**

         * mock method for ignore the permission check.

         * @param perm

         *            the requested permission.

         */

        @Override

        public void checkPermission(Permission perm) {

            // does nothing

        }



        /**

         * mock method for ignore the permission check.

         * @param perm

         *            the specified permission

         * @param context

         *            a system-dependent security context.

         */

        @Override

        public void checkPermission(Permission perm, Object context) {

            // does nothing

        }

    }
这个是测试用的方法：

    /**

     * execute the CommandLineClass.main method and check the exit status.

     * @param args

     *            the arguments for the main method

     * @param expectedStatus

     *            the expected exit status

     */

    private void assertExecuteStatus(String[] args, int expectedStatus) {

        // backup the security manager.

        SecurityManager oldManager = System.getSecurityManager();

        MockSecurityManager manager = new MockSecurityManager();

        System.setSecurityManager(manager);

        try {

            CommandLineClass.main(args);

        } catch (SecurityException e) {

            // ignore

        }

        assertEquals("the return status should be " + expectedStatus, expectedStatus, manager.getStatus());

        // restore the security manager

        System.setSecurityManager(oldManager);



    }