Add some test for timestamp

[methane]

No description provided.

[codecov-io]

Codecov Report

Merging #403 into master will decrease coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #403      +/-   ##
==========================================
- Coverage    87.7%   87.58%   -0.12%     
==========================================
  Files           5        5              
  Lines         846      846              
==========================================
- Hits          742      741       -1     
- Misses        104      105       +1

Impacted Files	Coverage Δ
msgpack/fallback.py	88.39% <100%> (-0.42%)	⬇️
msgpack/ext.py	85.18% <0%> (+2.46%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ff1f5f8...e2c13db. Read the comment docs.