Tests for L2EthToken.sol Contract

[neotheprogramist]

fixes neotheprogramist#2

[AntonD3]

Overall tests look good, I left some small comments about the code itself. And can you add some more test cases:

• For simple methods: balanceOf, decimals, symbol, and name. Maybe just one simple test case per each. I understand that their logic is pretty simple, but it can help to catch some issues with interface changes, getters, etc.
• Negative test cases, for example, when mint is called by not bootloader. balanceOf with dirty bytes. And maybe you can think about withdraw.

Apart from that, usually we have another test structure - a separate describe block per each external function. You can have a look at the contract deployer test, for example. IMHO, it makes the test more structured and readable. But if you have another opinion - I am open to discussing it.

[AntonD3]

Nice, LGTM! Left only a few small comments. And can you please add just some simple test for the totalSupply getter? Sorry, forgot about this getter during the previous review.