make unit test a little bit more stable

[shalehaha]

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #601 (0507787) into dev-v3.1.2 (138bde8) will increase coverage by 0.00%.
The diff coverage is 81.25%.

@@             Coverage Diff             @@
##           dev-v3.1.2     #601   +/-   ##
===========================================
  Coverage       85.28%   85.29%           
===========================================
  Files             102      102           
  Lines            4552     4567   +15     
===========================================
+ Hits             3882     3895   +13     
- Misses            670      672    +2