refactor(RestructuredTest): rename variable, fix typo and remove unne…

[bearomorphism]

…cessary string copy

Description

• Rename variables
• Fix the unbounded variable index
• Make some methods module functions
• Fix typo
• Remove the use of string slice (e.g. first[1:]) because it causes extra string copy

Similar changes in #1596

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.25%. Comparing base (120d514) to head (928af2d).
⚠️ Report is 805 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1609      +/-   ##
==========================================
+ Coverage   97.33%   98.25%   +0.91%     
==========================================
  Files          42       58      +16     
  Lines        2104     2690     +586     
==========================================
+ Hits         2048     2643     +595     
+ Misses         56       47       -9     

Flag	Coverage Δ
unittests	98.25% <100.00%> (+0.91%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.