How to test the when step in a stage about jenkinspipelineunit HOT 2 CLOSED

helper.registerAllowedMethod('environment', [Map.class], {it -> (it.value == binding.getProperty('env')[it.name]) })

helper.registerAllowedMethod('when', [Closure.class], {c -> 
    if(!c.call()){
         throw new Exception("conditional check failed")
    } 
})

helper.registerAllowedMethod('stage', [String.class, Closure.class], {s, c -> 
     try {
          c.call()
     } catch(Exception e) {
          if(!e.message.contains("conditional check failed")) {
             throw e
         }
     }  
})