run-tests: report tests that exception occurred in We now record the test that an exception occurred in. We put this information to use by aggregating the count of failures in each test. For each exception, the exception report now prints the total number of tests having that exception and the test with the least number of exceptions exhibiting that failure. The exception list is now sorted by (total count, tests impacted, count of failures in least failing test). This allows us to: * Assess how widespread a failure is. Some exceptions occur a lot in a few tests. Others occur over many tests. * Easily run a test exhibiting an exception without having to find a failure in test output. * Find and fix low hanging fruit (e.g. exceptions that are the only failure in a test). Here's an example of the new output: 199 (4 tests) /home/gps/src/hg/hgext/blackbox.py:191: %b requires a bytes-like object, or an object that implements __bytes__, not 'str' (test-devel-warnings.t - 1 total) 142 (19 tests) /home/gps/src/hg/hgext/mq.py:655: list indices must be integers or slices, not bytes (test-hardlinks.t - 1 total) 140 (20 tests) /home/gps/src/hg/mercurial/patch.py:296: string argument expected, got 'bytes' (test-audit-subrepo.t - 1 total) 101 (15 tests) /home/gps/src/hg/hgext/convert/convcmd.py:60: encode() argument 1 must be str, not bytes (test-convert-clonebranches.t - 1 total) 90 (2 tests) /home/gps/src/hg/hgext/mq.py:456: can't concat str to bytes (test-mq-qqueue.t - 1 total) 87 (2 tests) /home/gps/src/hg/mercurial/branchmap.py:380: %b requires a bytes-like object, or an object that implements __bytes__, not 'FileNotFoundError' (test-branches.t - 2 total) 85 (22 tests) /home/gps/src/hg/mercurial/sshpeer.py:223: cannot convert 'UUID' object to bytes (test-bundle2-pushback.t - 1 total) 1 (1 tests) /home/gps/src/hg/mercurial/formatter.py:254: %b requires a bytes-like object, or an object that implements __bytes__, not 'str' (test-debugextensions.t - 2 total) 1 (1 tests) /home/gps/src/hg/hgext/convert/convcmd.py:420: startswith first arg must be str or a tuple of str, not bytes (test-convert-authormap.t - 2 total) 1 (1 tests) /home/gps/src/hg/mercurial/revlog.py:797: '>=' not supported between instances of 'NoneType' and 'int' (test-unionrepo.t - 1 total) 1 (1 tests) /home/gps/src/hg/hgext/show.py:129: %b requires a bytes-like object, or an object that implements __bytes__, not 'str' (test-show.t - 1 total) Differential Revision: https://phab.mercurial-scm.org/D2138