test: add unit tests for core/resolver.js

[cuixiaorui]

Types of changes

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

Description

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: #)
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[codecov-io]

Codecov Report

Merging #5790 into dev will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev    #5790      +/-   ##
==========================================
+ Coverage   95.64%   95.67%   +0.03%     
==========================================
  Files          82       82              
  Lines        2662     2662              
  Branches      682      682              
==========================================
+ Hits         2546     2547       +1     
+ Misses         98       97       -1     
  Partials       18       18

Flag	Coverage Δ
#e2e	100% <ø> (ø)	⬆️
#fixtures	50.71% <ø> (ø)	⬆️
#unit	92.63% <ø> (+0.03%)	⬆️

Impacted Files	Coverage Δ
packages/core/src/resolver.js	100% <0%> (+1.56%)	⬆️

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[clarkdo]

@cuixiaorui Tips: For tests change, please use test: as the type of pr title.