Add some tests and improve others to raise coverage percentage. This
should lead to almost 100% for the AbuseFilterParser class. Aside from
this, a couple of changes:
* Remove an unused function
* Let equals_to_any return a genuine result with empty strings
* Remove an if which will never be true in skipOverBraces, since the
function is called after checking the same conditions.
Bug: T201193
Change-Id: I7020b2ed996236c38c5784d161ad98ec44163406
Introduce a new function which can be used to group multiple comparisons
in a single condition. In particular, equals_to_any(S, A, B) is the
equivalent of S === A || S === B. This is especially useful in checking
for multiple namespaces, as proposed in the Community health initiative.
Change-Id: I9dcfe303eb5e51e1882fe4a65fa876aa93db7686
