Increase Coverage

[alganet]

• Changed Property so it doesn't have an unreachable line anymore.
• Rename ValidatorTest to ValidatorBuilderTest to better reflect the source.
• Added missing tests for KeyExists's ArrayAccess support.
• Added tests for using custom exceptions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.48%. Comparing base (b352f17) to head (1e13ad7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1660      +/-   ##
============================================
+ Coverage     99.29%   99.48%   +0.18%     
  Complexity      920      920              
============================================
  Files           190      190              
  Lines          2141     2143       +2     
============================================
+ Hits           2126     2132       +6     
+ Misses           15       11       -4     

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