tests: raise a better error when patterns are wrongly formatted
It is fairly easy to make mistakes when merging conflict in the pattern file.
A common mistake is to forget adding an extra trailing comma changing the
length of the tuple.
We now detect such error and raise a better error message that helps to find
it.
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present