SyntaxError.
This is probably not the proper solution to this failing test, but removing the
test itself causes 19 other tests to fail for some odd reason because doctest
doesn't expect a complete traceback (or something; rather odd problem for just
removing a single test).
>>> `1` = 1
Traceback (most recent call last):
-SyntaxError: can't assign to repr (<doctest test.test_syntax[10]>, line 1)
+SyntaxError: invalid syntax
If the left-hand side of an assignment is a list or tuple, an illegal
expression inside that contain should still cause a syntax error.