revlog: test that pending hooks properly see the repository on split This seems important to explicitly cover this case before changing the code.

revlog: test possible read race condition with splitting This is currently working fine, but could break with another approach (for example, with the one we are about to use in the next changesets…) So we make sure the case is covered.

revlog: add a failing variant of the the split + transaction test We have another variant to tests, and it is crashing… So lets cover it with tests.

revlog: update the split + transaction test We add section, increase the amount of comments and simplify some of the constructs. We are about to build more on top this tests so lets do a small cleanup first.

transaction: allow to backup file that already have an offset This will be useful in the next changeset to deal with rolling back the split of inline revlog on transaction failure. This involve deeper change to the transaction logic as we need to make sure we restore the backup -before- the truncation step. Otherwise, the truncation would act on the wrong file and be overwritten by the backup restoration later.

transaction: move the restoration of backup file in a small closure We are about to use that logic in two different location, making is a small reusable closure prepares that.