Add page tests

[johnfercher]

Description

• Add page unit tests

Related Issue

Checklist

check with "x", if applied to your change

• All methods associated with structs has func (<first letter of struct> *struct) method() {} name style.
• Wrote unit tests for new/changed features.
• Followed the unit test when,should naming pattern.
• Updated docs/doc.go and docs/*
• Updated pkg/pdf/example_test.go
• Updated README.md
• Executed make examples to update all examples inside docs/examples.
• New public methods/structs/interfaces has comments upside them explaining they responsibilities
• Executed make dod with none issues pointed out by golangci-lint

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (21b2202) 79.84% compared to head (054319e) 81.57%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #391      +/-   ##
==========================================
+ Coverage   79.84%   81.57%   +1.74%     
==========================================
  Files          61       61              
  Lines        2018     2018              
==========================================
+ Hits         1611     1646      +35     
+ Misses        379      345      -34     
+ Partials       28       27       -1     

Flag	Coverage Δ
unittests	81.57% <ø> (+1.74%)	⬆️

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