Use month with 31 days to avoid test failures

[gutsytechster]

The test fails on the 31st of any month since the set month in the test doesn't have the 31st date. We fix this by using the month with 31 days.

Fixes #1053

[codecov]

Codecov Report

Base: 98.23% // Head: 98.23% // No change to project coverage 👍

Coverage data is based on head (1369aa2) compared to base (c30d8c0).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1086   +/-   ##
=======================================
  Coverage   98.23%   98.23%           
=======================================
  Files         232      232           
  Lines        2599     2599           
=======================================
  Hits         2553     2553           
  Misses         46       46           

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