optimize tx parallel execution ut

[LeoGuo621]

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)

[codecov-commenter]

Codecov Report

Merging #3203 (a08b465) into dev (39c86b1) will increase coverage by 0.11%.
The diff coverage is 92.59%.

❗ Current head a08b465 differs from pull request most recent head f6b2fd9. Consider uploading reports for the commit f6b2fd9 to get more accurate results

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@@            Coverage Diff             @@
##              dev    #3203      +/-   ##
==========================================
+ Coverage   36.46%   36.57%   +0.11%     
==========================================
  Files         444      444              
  Lines       46606    46633      +27     
==========================================
+ Hits        16993    17056      +63     
+ Misses      28347    28310      -37     
- Partials     1266     1267       +1     

Impacted Files	Coverage Δ
app/test_helpers.go	92.15% <92.59%> (+0.49%)	⬆️

... and 2 files with indirect coverage changes