Increase some modules housed in the worker directory unit test coverage

[tunedev]

This aims to increase the below-listed modules file path's test coverage

Context

The modules are all under the caliper-core/lib/worker directory
Related to #1557

Expected Behavior

After running the tests in caliper-core the below listed %stmts in the code coverage report should tally with the below listed

• caliper-core/lib/worker/caliper-worker.js: 82
• caliper-core/lib/worker/worker-message-handler.js: 9.78
• caliper-core/lib/worker/fixedFeedbackRate.js: 60
• caliper-core/lib/worker/recordRate.js: 43.28
  

Actual Behavior

After running the tests in caliper-core the below listed %stmts in the code coverage report the below listed was what was there before

• caliper-core/lib/worker/caliper-worker.js: 93.75
• caliper-core/lib/worker/worker-message-handler.js: 89.13
• caliper-core/lib/worker/fixedFeedbackRate.js: 80
• caliper-core/lib/worker/recordRate.js: 95.52
  

Possible Fix

Steps to Reproduce

Existing issues

• Stack Overflow issues
• GitHub Issues
• Discord Chat history

Context

Your Environment

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