[Python-Dev] I am now lost - committed, pulled, merged, what is "collapse"?

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    Stephen> Subversion merges create new versions in the repository that
    Stephen> *never existed in any developer's workspace* and therefore was
    Stephen> never tested before committing.  This is somewhat mitigated by
    Stephen> buildbot testing, but that is mostly unit testing and
    Stephen> inherently is not very good at catching problems due to
    Stephen> interactions across modules.  That is, it's not that Subversion
    Stephen> provided a simpler way of doing the work.  Rather, it hid the
    Stephen> fact that certain work was not being done at all.  hg exposes
    Stephen> this fact.

Can you provide an example of this (real or hypothetical)?  It seems to me
that if all you have is unit tests it matters little, if at all, whether you
catch test failures before a checkin (in your local hg repo) or after (using
svn + a buildbot run).  The workflow of the version control system isn't
going to magically expose semantic interactions across modules.  It seems to
me that at best the new workflow means there is a better chance of catching
textual conflicts before checkin than before.

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