Add tests for empty container, page size, and summary tag values; enhance immutability checks.

[terabytesoftw]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.83%. Comparing base (17bb2ef) to head (8c66448).
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #272      +/-   ##
============================================
+ Coverage     83.66%   84.83%   +1.17%     
  Complexity      629      629              
============================================
  Files            50       50              
  Lines          2136     2136              
============================================
+ Hits           1787     1812      +25     
+ Misses          349      324      -25     

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