Cover transaction manager with additional test cases

[dshulyak]

Problem

Transaction manager (txqueue_manager.go) should be covered with additional test cases to ensure that it won't get accidentally broken after next changes.

Test cases that are currently missing:

1. Verify that gas value and gas price is not ignored if received from a user
2. Verify that a transaction is signed as we expect it to be signed

Implementation

1. We definitely need to have additional test case with gas and gas price defined by a user. Might be 2 different test cases or 1 with both values defined.
2. Second part of the issue is about verifying that we are sending transaction that we are expecting to send. I was planning to prepare a Transaction with all expected values, sign it the same way we do in transaction manager, rlp encode and provide as an expected value to a mock.

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[canercidam]

Here's what I have in mind:

1. A transaction is object is initialized.
2. Gas price is set to a non-nil value.
3. Gas is set to a non-nil value larger than default value.
4. Transaction is used by CompleteTransaction and an identical copy is signed externally.
5. Transaction hashes are compared.

How does it sound? And the test function could be called TestCompletionValidity since it covers both of the behaviours.

[dshulyak]

That's close but not exactly. For the second part, I was planning to have a piece of code that will be used for every test case that completes a transaction. This piece of code can use transaction as an input and will prepare mocks for geth rpc api. Take a look at setupTransactionPoolAPI in tests for transactions manager

[canercidam]

Ah okay, I see what you mean now. I'll start getting a PR ready in a bit.

[canercidam]

@dshulyak I don't believe I solved it the way you imagined but this looked like the best way to me.