[MERGE] Add PreviewTree to the tree implementation tests

[Tim Penhey]

On Monday 28 April 2008 15:06:29 Aaron Bentley wrote:
> Hi all,
> 
> This patch is an update of my earlier one, with test_inv_alternatives
> merged back into test_inv, to address Andrew Bennett's concerns.
> 
> Aaron

Does this mean that a PreviewTree can be used as a merge source
now?

What I want to be able to do is to have two related branches, branch1
and branch2, where branch2 was a continuation of branch1 where
branch1 may have had other commits.

Right now we can go:
  bzr merge --preview -d target-branch branch1
to get the diff that would be generated if branch1 was merged into branch2.

What I'd like to be able to do is to go
  bzr merge --preview -d target-branch branch1 branch2 (or something)
that would first do an "in memory merge" of branch1 into target-branch,
and then use that to generate a preview for branch2 being merged into
this.

The use case for this is where you are working on a big(ish) feature and
you are wanting to break up the branch for review purposes.  So you might
have a series of branches: branch1, branch2, branch3, and you are wanting
to generate a diff for review for branch3, based upon what the target-branch
would look like if branch2 was already merged in.

Tim