Hi Martin, Brett:

On Sun, May 8, 2016 at 10:38 AM, Brett Cannon <brett@python.org> wrote:
$ git rev-list --count master

I don’t know what the equivalent command in Mercurial is. Perhaps you
could clone the relevant branch to a fresh repository and check the
numerical revision number.

SO to the rescue (and Martin is right about how to figure it out): http://stackoverflow.com/questions/16672788/total-count-of-change-sets-for-mercurial-and-git

Senthil has also suggested verifying the hashes of all the files in a repository that are not in .hg or .git directories.

Are these validations enough for our purposes? 

Two files in the different version-control system can have same SHA and same commit of commits, but have a possibility of changesets/diffs associated with those commits different. I was thinking, how we should go about with this when evaluating the existing git repo.

When we do migration afresh using a tool like hg-git, we assume that this verification step is asserted as part of unit tests of the tool.