[qmtest] Upgrading tests

[Vladimir Prus]

Mark Mitchell wrote:
> > Is something like this available somewhere, or planned?
>
> No, there's nothing like that available, but it is a good idea.
>
> It should not be too hard to write a method that iterates over each test
> in a database, and rewrites the test.

Okay, I've implemented this, and successfully processed around 70 tests -- 
which would be pain to upgrade manually.

The way upgrading works with my implementation is quite simple. If a user 
wants to change some test class, say "History", he first writes new class 
"History2". The new class, besides other methods, should have 'Upgrade' 
method. He tests the new class on a couple of tests -- which must be manually 
upgraded, and they runs
 
   qmtest ...  upgrade-tdb 
             --from some_module.History --to some_module.History2

The upgrade logic is
1. Old test is loaded
2. Instance of new test class is created
3. Method 'Upgrade' on the new instance is called with the old class instance
4. The test is saved.

I'd be happy to send the patch, if there's interest, but there are two things 
I don't like and would prefer to cleanup -- and that requires some 
discussion.

First, problem is that database can't save tests, only instances of 
TestDescriptor. I'm thinking that either database should be able to save 
tests, too, or there should be a method in  Test which return TestDescriptor. 

The biggest problem is that it's hard to create default-initialized instance 
of new test class. I can pass empty mapping for arguments, but 
Runnable.__init__ expects 'extra' keyword arguments. I can work around this, 
too, by passing what Runnable expects, but this starts to be rather messy. 
E.g., if Runnable is changes to require another extra keyword argument, my 
code will break. Is there some way I can cleanly create default-initialized 
test instance?

- Volodya