Test for Bitcoin Fungible transfer

[wainola]

Provide test for BTC Fungible class.

Implementation details

• Define mocks if necessary for the different methods or functons being used
• Test cases for miner fee calculation and transaction creation
• failing and success conditions

Testing details

Acceptance Criteria

• Bitcoin Fungible class and related functions are tested and all test are passing

QA Details

[wainola]

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