Refactor tests of StringExtension::truncate_bytesize
Refactor tests of StringExtension::truncate_bytesize

Move all relevant assertions to one test method.
Delete tests of Ruby methods.

raysuelzer/mushroom-observer,pellaea/mushroom-observer,raysuelzer/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,raysuelzer/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,raysuelzer/mushroom-observer,MushroomObserver/mushroom-observer,raysuelzer/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,raysuelzer/mushroom-observer,raysuelzer/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer