Add unit tests for apostrophe operator

[sequba]

Context

How has this been tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature or improvement (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Additional language file or change to the existing one (translations)

Related issue(s):

1. Docs: document apostrophe as an explicit string literal trigger #960

Checklist:

• My code follows the code style of this project,
• My change requires a change to the documentation,
• I described the modification in the CHANGELOG.md file.

[codecov]

Codecov Report

Merging #969 (00da2cf) into develop (0c1e9ff) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #969   +/-   ##
========================================
  Coverage    95.73%   95.73%           
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  Files          161      161           
  Lines        14056    14056           
  Branches      2911     2911           
========================================
  Hits         13456    13456           
  Misses         600      600           

[sequba]

Tests will be added in #1161