Improve code coverage for elements and framework

Currently, there are few unit tests missing for elements and framework files which can be improved through code refactoring and test coverage phase.

Most of these files have covered the function level unit test, the majority of missing coverage or related to branching.

To improve the code coverage with unit test

Add missing unit test for empty signature ['mk','mk', '', 'ok', '','ok'] scenario in utils/verify/verifyMultiSignatureTransaction
elements/lisk-cryptography/src/buffer.ts intToBuffer
elements/lisk-cryptography/src/encrypt.ts
elements/lisk-bft/src/bft.ts
elements/lisk-chain/src/block_reward.ts
elements/lisk-chain/src/verify.ts
elements/lisk-chain/src/chain.ts
elements/lisk-chain/src/data_access/data_access.ts
elements/lisk-chain/src/data_access/cache/base.ts
elements/lisk-chain/src/state_store/state_store.ts
elements/lisk-chain/src/state_store/chain_state_store.ts
elements/lisk-chain/src/state_store/transaction_store.ts
elements/lisk-chain/src/transactions/exceptions_handlers.ts
elements/lisk-dpos/src/delegates_info.ts
elements/lisk-validator/src/validation.ts
framework/src/application/application.js
framework/src/application/network/network.js
framework/src/application/configurator/configurator.js
framework/src/application/node/block_processor_v0.js
framework/src/application/node/node.js
framework/src/application/node/rebuilder.js
framework/src/application/node/forger/forger.js
framework/src/application/node/forger/sort.js
framework/src/application/node/processor/pipeline.js
framework/src/application/node/synchronizer/fast_chain_switching_mechanism.js
framework/src/application/validator/formats.js
framework/src/controller/bus.js
framework/src/controller/controller.js
framework/src/controller/channels/in_memory_channel.js

These list was identified by going through the code coverage on sdk development branch from jenkins https://jenkins.lisk.io/job/lisk-sdk/job/development/86/cobertura/

Before we start working on this issue, we can have a discussion on which ones to cover and split the issue into multiple accordingly, also eliminate the once which need not required to cover.

LiskArchive / lisk-sdk