我正在为一个插件创建一个测试用例，我想获取当前Jenkins服务器上存在的所有环境变量。谁能告诉我如何从Jenkins服务器获取所有环境变量？

public class VariableExistsConditionTest {

    @Rule public JenkinsRule j = new JenkinsRule(); 

     @Test
      public void someTest() throws IOException, InterruptedException {
         EnvironmentVariablesNodeProperty prop = new EnvironmentVariablesNodeProperty();
         EnvVars env = prop.getEnvVars();
         env.put("DEPLOY_TARGET", "staging");
         j.jenkins.getGlobalNodeProperties().add(prop);
        //Code to fetch the environment variables

}