tests: switch asserts to require

[ValarDragon]

Is there a reason we use asserts in most tests instead of require? I find it much harder to debug the output of assert statements (since it takes longer to isolate the actual error), and I think it just increases time to debug the core issue. I propose that we change all of the assert statements in test cases to requires. Should be do-able with a couple of sed commands.

(Assert still executes the remaining tests, whereas require halts after that error)

/cc @ebuchman , @rigelrozanski , @cwgoes

[rigelrozanski]

yeah totally let's replace the majority of asserts with requires - asserts can still be useful in limited scenarios - for instance, you want to check a series of parameters from the output simultaneously - if you used require there it could be difficult to adequately debug.