Pallet Unit Tests concerning Balances: Modify mock.rs to have ED > 1, to test balances less than ED.

[mattheworris]

As a developer, I would like to create some unit tests for situations when the account balance is less than the Existential Deposit (ED).

Currently, the mocks has ED == 1, so it is not possible to test any situations where ED < 1, which some valid edge cases do exist.

• [ ] Modify mock.rs to have ED > 1
• [ ] Modify unit tests that are affected by this change.