Speed up tests slightly by using constants
Speed up tests slightly by using constants

Previously we did disk I/O on each Reader presenter test to load data
that was constant over all tests. This refactors the tests to do the I/O
only once, and use "const" to make sure test pollution doesn't take
place.

[endlessm/eos-sdk#2681]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib