Bangaldesh have improved significantly in recent times, and they are infinitely better than Kenya at this stage. In saying that, given the time, support, infrastructure, stability and opportunities Bangladesh have been given, I'm of the opinion that Kenya would be at a higher level of aptitude than Bangladesh right now.. but that didn't happen so it's useless discussing such.
Kenya may have a pretty solid side, but they really aren't good enough for test cricket. Bangladesh quite obviously aren't either, however the signs are there that they are improving to such a standard - their players are young, their Under 19s carve up, the have money in the game there, they have a stable system and they have the infrastructure available to progress. Kenya don't have any of these things really.
Zimbabwe is a totally different story, but it's just that - totally different. Remove the political woes of the country and they'd be as good as the West Indies IMO - as it is, they shouldn't be near test cricket though... Scotland and Ireland would even be better candidates than Zim at this stage IMO, but once you give test status to a team, it's hard to take it away.