## What is the purpose of the change 为HeaderExchangeChannel类写单元测试
## Brief changelog 测试了如下方法： - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#send(java.lang.Object) - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#request(java.lang.Object) - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#getOrAddChannel - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#close(int) - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#isConnected - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#getAttribute - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#removeAttribute - org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeChannel#removeChannelIfDisconnected ## Verifying this change Dubbo 单元测试的开发是基于单元测试框架 junit 4 1、Mock 框架 mockito 2来完成的。具体代码编写于HeaderExchangeChannelTest类。 Follow this checklist to help us incorporate your contribution quickly and easily: - [x] Make sure there is a [GITHUB_issue](https://github.com/apache/incubator-dubbo/issues) filed for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue. - [x] Format the pull request title like `[Dubbo-XXX] Fix UnknownException when host config not exist #XXX`. Each commit in the pull request should have a meaningful subject line and body. - [ ] Write a pull request description that is detailed enough to understand what the pull request does, how, and why. - [ ] Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in [test module](https://github.com/apache/incubator-dubbo/tree/master/dubbo-test). - [x] Run `mvn clean install -DskipTests` & `mvn clean test-compile failsafe:integration-test` to make sure unit-test and integration-test pass. - [ ] If this contribution is large, please follow the [Software Donation Guide](https://github.com/apache/incubator-dubbo/wiki/Software-donation-guide). [ Full content available at: https://github.com/apache/incubator-dubbo/pull/2373 ] This message was relayed via gitbox.apache.org for [email protected]
