tests: make doctests not depend on str(ParseError()) format

tests: make doctests not depend on str(ParseError()) format

`ParseError` implements `__bytes__`, but it doesn't implement
`__str__`, so it gets the default `__str__` implementation. The next
patch will make it so `ParseError` gets a `__str__` implementation,
which changes the format slightly. This prepares by making us not
depend on the format.

Differential Revision: https://phab.mercurial-scm.org/D9349

--- a/mercurial/revsetlang.py	Fri Nov 20 09:17:38 2020 -0800
+++ b/mercurial/revsetlang.py	Fri Nov 20 13:24:45 2020 -0800
@@ -558,14 +558,22 @@
 
     >>> _parsewith(b'foo($1)', syminitletters=_aliassyminitletters)
     ('func', ('symbol', 'foo'), ('symbol', '$1'))
-    >>> _parsewith(b'$1')
-    Traceback (most recent call last):
-      ...
-    ParseError: ("syntax error in revset '$1'", 0)
-    >>> _parsewith(b'foo bar')
-    Traceback (most recent call last):
-      ...
-    ParseError: ('invalid token', 4)
+    >>> from . import error
+    >>> from . import pycompat
+    >>> try:
+    ...   _parsewith(b'$1')
+    ... except error.ParseError as e:
+    ...   pycompat.sysstr(e.message)
+    ...   e.location
+    "syntax error in revset '$1'"
+    0
+    >>> try:
+    ...   _parsewith(b'foo bar')
+    ... except error.ParseError as e:
+    ...   pycompat.sysstr(e.message)
+    ...   e.location
+    'invalid token'
+    4
     """
     if lookup and spec.startswith(b'revset(') and spec.endswith(b')'):
         lookup = None

--- a/mercurial/templater.py	Fri Nov 20 09:17:38 2020 -0800
+++ b/mercurial/templater.py	Fri Nov 20 13:24:45 2020 -0800
@@ -376,14 +376,22 @@
     ('string', 'foo')
     >>> parseexpr(b'foo(bar)')
     ('func', ('symbol', 'foo'), ('symbol', 'bar'))
-    >>> parseexpr(b'foo(')
-    Traceback (most recent call last):
-      ...
-    ParseError: ('not a prefix: end', 4)
-    >>> parseexpr(b'"foo" "bar"')
-    Traceback (most recent call last):
-      ...
-    ParseError: ('invalid token', 7)
+    >>> from . import error
+    >>> from . import pycompat
+    >>> try:
+    ...   parseexpr(b'foo(')
+    ... except error.ParseError as e:
+    ...   pycompat.sysstr(e.message)
+    ...   e.location
+    'not a prefix: end'
+    4
+    >>> try:
+    ...   parseexpr(b'"foo" "bar"')
+    ... except error.ParseError as e:
+    ...   pycompat.sysstr(e.message)
+    ...   e.location
+    'invalid token'
+    7
     """
     try:
         return _parseexpr(expr)