What is the purpose of the change

#1689: Enhance the test coverage part-10 : dubbo-plugin module

Brief changelog

dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/command/CommandContextFactoryTest.java
dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/command/CommandContextTest.java
dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/command/DefaultCommandExecutorTest.java
dubbo-plugin/dubbo-qos/src/test/java/org/apache/dubbo/qos/command/GreetingCommand.java
dubbo-plugin/dubbo-qos/src/test/resources/META-INF/services/org.apache.dubbo.qos.command.BaseCommand

Verifying this change

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