Review unit test coverage of logic

[karmacoma]

Parent: #1169

List of child issues:

• Review unit test coverage for logic/account Review unit test coverage for logic/account #1599
• Review unit test coverage for logic/block_reward Review unit test coverage for logic/block_reward #1600
• Review unit test coverage for logic/block Review unit test coverage for logic/block #1601
• Review unit test coverage for logic/transaction Review unit test coverage for logic/transaction #1602
• Add unit tests for logic/broadcaster Add unit tests for logic/broadcaster #1625
• Consistent usage of es6 features in logic implementation Consistent usage of es6 features in logic implementation #1656
• Review unit test coverage for logic/transaction_pool Review unit test coverage for logic/transaction_pool #1662
• Review unit test coverage of logic/vote Review unit test coverage of logic/vote #1663

[toschdev]

I'd like to have a word how this might be correlated with work on lisk-js. Whoever works on this, please drop a message to me as soon as you start :)

[ManuGowda]

@Tosch110 I have taken this issue, just letting you know if you want to discuss anything down the line.