Hi
What you need to do is make Test Attributes generate an error if it it turns out false AND configure error handling to skip the current branch on error.
Do as follows:
1. select the Test Attributes step, select the tab named Error Generation, and check the box.
2. select the tab Error Handling and configure Own Errors to Ignore and Skip Branch.
Now if the two attributes are the same the iteration of the loop will be skipped.
"Any ideas to store previous output object and compare it with current output object...?"
I think global variables is the right way to do this. you are doing the right thing in your robot but I think you will have to rearrange your steps a bit. ex. Test Attribute is failing on first iteration.
-Simon