index_bounds_test.cpp does a good job at covering different scenarios for IndexBounds::isValidFor method but only does it with normal indexes, majority of special indexes such as geo, text, column, etc... are missing. Essentially we need to cover all indexes listed here: https://github.com/10gen/mongo/blob/425972f1d9496ce7cbb6a2b24d1e4636e962f7ad/src/mongo/db/index_names.h#L43