[all][conf] test cases for values retrieved from conf

[mocchira]

Not to overlook kinda #586 . Also maybe adding the feature that enumerating the all keys in conf and check whether their key name really exist or not would be helpful not only for devs but for users who might typo keys. (also https://en.wikipedia.org/wiki/Levenshtein_distance would give us more help to suggest closest matches to typo.