Add collapse_if_tuple test cases

[davesque]

What was wrong?

The test cases for collapse_if_tuple did not cover two edge cases.

How was it fixed?

Added tests for them.

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[carver]

Nice, yeah it seemed apparent that it would work, but it's nice to have in place to prevent regressions.

[pipermerriam]

It looks like the docs don't know anything about this function, should it be added or is it private API?

[davesque]

@pipermerriam Not sure. It's in a kind of weird gray area. To me, it seems rather specific to the particular problem we're trying to solve in web3.py. In that way, I feel like it doesn't belong in eth-utils. On the other hand, it is used in eth_utils.abi._abi_to_signature. It's also used in web3._utils.abi. Perhaps we could go ahead and make it private with an underscore prefix since the only place it's used outside of eth-utils is in a private utility module in web3.py.

[pipermerriam]

@carver what do you think about leaving it in a weird limbo for now, not documenting publicly but exposing without an _ prefix as if it was a public API.

[davesque]

@pipermerriam @carver Actually, now I don't like the idea I was proposing. It would be nice to expect that anything underscore prefixed is not used outside of a package or module.

[davesque]

@pipermerriam @carver I created a separate issue ticket for this discussion.