The convenience of going back in time

Eclipse has a really nice feature called “Local History”.  Allow me to demonstrate how it helped me just now:

We have a TransactionManager class that provides the ability for writers of integration tests who are writing tests below the level where AOP transaction advice is automatically applied, to just do basic getTransaction(), commit() and rollback() operations without worrying about the details of the underlying Spring PlatformTransactionManager.

Once you instantiate our TransactionManager, it holds a reference to the PlatformTransactionManager bean.

It’s possible for a test writer to have a situation where they reinitialize the Spring application context but are still holding onto a PlatformTransactionManager bean reference from the prior instantiation.  These developers don’t tend to focus their energies on such low-level issues like we Framework guys do, so it could be quite a time-waster if it resulted in an obscure error they had to debug to get to the root of — we’d rather detect the situation and throw a more descriptive error.

To that end, I had started yesterday morning writing a test that would show what currently happens in this scenario, in preparation for changing the code to do the detect-n-throw.

After this start though, I spent most of the day doing training.   It was fun!  But an interesting thing about doing interactive training with code examples: by the time it was all done, my Eclipse workspace was in quite an odd state!  Tests failing, things not compiling — because in the process of explaining I would just go try things here and there.  Afterward, the best thing to do was just revert everything back to what was in the repository.

Today I looked at my test class for the TransctionManager and noticed that my work on the scenario I’ve described was gone.  “Ah yes, I reverted the source…” I mused.  I started to type it in again, but it required enough thinking about what calls the mocks should expect, that I hesitated, and remembered Local History.

Local history records a snapshot each time you save, and I save changes so often that a lot of times it’s hard to find just the local revision I need…

I decided to try it anyway.  I right-clicked on my TransactionManagerTest and chose Compare With -> Local History…

This added the History view, and I expanded Yesterday…

Notice the several saves leading up to 8:49 AM, and then the lone change at 3:16 PM.  3:16 PM looks like the revert, so let’s double-click on the 8:49 AM one to compare…

(The whitish bars along the right-hand side show where differences are.  Bigger changes show up as bigger whitish bars.  I clicked on the largish bar near the bottom.)

This is the method I coded yesterday!  Let’s put it back in the source: while it’s selected, press the “Copy Current Change from Right to Left” button, and…

There we are…beautiful!

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