Assert keeps going after failure, but require immediately fails
the tests, making it easier to find the output related to the test
failure, rather than having to comb through a bunch of subsequent
assertion failures. For equality tests, we may or may not want to
continue, but for error checks we almost always want to immediately
fail the test. Exceptions can be changed as-needed.
The FieldPath was not being set for nodes underneath a SequenceNode
during fieldspec's traversal. This is in part because handleSequence
uses VisitElements in contrast to a PathGetter as is done by handleMap.
The accuracy of FieldPath is more relevant now with the recently added
support of mutation trackers in filtersutil. This change fixes the
case where a mutation tracker callback is called on a SequenceNode
element and the node does not have an accurate FieldPath value.
