[CSE-226] Mock test data of an empty slot
[CSE-226] Mock test data of an empty slot

and a failure of searching for `epoch`/`slot`

input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl