Unsufficient tests for Python reader and writer.

[boxdot]

Right now, we have generated reader tests (in Python) for the C++ byte reader. The problem is, that they always try to read 1 from the beginning of some data segment, never deeper in the data. In particular, they test that we read correcly with varying bit_size but not varying offset. Note, when reading 1, the bit_size is not really significant.

Generated writer tests are missing completely.

[VeaaC]

Do you mean insufficient python tests? The C++ tests test all offsets with all bit widths, and test the highest bit possible for each.

[boxdot]

Yes, I mean Python tests.

[imagovrn]

@boxdot In general I agree with you. However, there are also backward-compatibility tests that are checking both signed and unsigned unaligned values, so it should be safe. This doesn't dismiss the point that we should improve the reader tests.