test: add unit tests for SDK

[chr1shung]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/device-sdk-c/blob/master/.github/CONTRIBUTING.md

What is the current behavior?

Issue Number:

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

New Imports

• Yes
• No

Specific Instructions

Other information

[codecov-commenter]

Codecov Report

Merging #900 (5fdfe4e) into master (edddd13) will increase coverage by 5.48%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #900      +/-   ##
==========================================
+ Coverage   34.29%   39.78%   +5.48%     
==========================================
  Files          26       28       +2     
  Lines        2146     2697     +551     
==========================================
+ Hits          736     1073     +337     
- Misses       1341     1529     +188     
- Partials       69       95      +26     

Impacted Files	Coverage Δ
internal/cache/init.go	0.00% <ø> (ø)
pkg/service/init.go	0.00% <0.00%> (ø)
internal/application/callback.go	0.00% <0.00%> (ø)
internal/application/command.go	28.21% <0.00%> (ø)
internal/transformer/transformresult.go	62.59% <0.00%> (+1.49%)	⬆️
pkg/models/commandvalue.go	83.97% <0.00%> (+75.60%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update edddd13...5fdfe4e. Read the comment docs.

[cloudxxx8]

LGTM