The MongoRunner test helpers take a "configuration object" rather than an array, which means for example that you cannot test passing the same command line option twice.
This line here, in the function that does the option conversion:
array is "object", so it doesn't work at all:
We should either delete this code or fix "isObject" so that it returns the correct thing. As it is now, this is effectively dead and misleading code. As part of this we need to decide whether MongoRunner should support arrays for configuration or not.