hook: add tests for failing post- python hooks I couldn't find any tests for this.

hook: even fewer parentheses for load errors Missed this one.

destutil: document various failure cases We document what various conditional branch mean and clarify that they are exclusive (since they all end up in with exception raised).

destutil: consistently retrieve 'p1' and 'branch' We already read p1 from the dirstate so let's read the branch from it too.

merge: give priority to "not at head" failures for bare 'hg merge' We refuse to pick a destination for a bare 'hg merge' if the working copy is not at head. This is meant to prevent strange merge from user who forget to update. (Moreover, such merge does not reduce actually the number of heads) However, we were doing that as the last possible failure type. So user were recommended to merge with an explicit head (from this bad location) if the branch had too many heads. We now make "not on branch heads" class of failure the first things to check and fail on. The one test that change was actually trying to check for these failure (and did not). The new test output is correct.

destutil: extract all 'mergedest' abort messages into a dictionary We plan to be able to reuse this function for rebase. The error message explicitly refers to "merge" in multiple places. So we'll need to be able to use different messages. The first step of that is to extract all messages in a dedicated dictionary and use them indirectly. As a side effect it clarifies the actual function and opens the way to various cleanups and fixes in future changesets.

tests: add an explicit destination in some rebase tests As we will make 'rebase' behave more like 'merge', it will no longer pick 'max(branch(.))' as the default destination. We have to hard code the expected destination is multiple tests where it matters. After a careful inspection none of theses tests really cares about the default destination behavior and just omitted one out of laziness.

tests: remove third head in some of the 'rebase-parameters' tests These tests do not care about that extra branch at all. In future changeset we will make rebase behave like merge and abort in case of an ambiguous destination (eg: multiple other heads) and that extra branch will make the command invocation breaks. We preventively remove this extra branch from the relevant tests in an independant changeset to reduce noise and increase confidence in the final change.

run-tests: allow to specify executable of any name by --with-hg If the executable is not named as "hg", TTest runner inserts alias. This way, we can run tests with chg. But it is still warned because the alias does not always work. We do "$BINDIR"/hg in a few places.

run-tests: drop redundant assignment to BINDIR We do it a few lines after.