Fix #7, update code coverage for md_app_tests.c

[havencarlson]

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution
Fix #7
Updated unit tests for md_app_tests.c for more coverage.

Testing performed

1. lcov --capture --rc lcov_branch_coverage=1 --directory build --output-file coverage_test.info
2. lcov --rc lcov_branch_coverage=1 --add-tracefile coverage_base.info --add-tracefile coverage_test.info --output-file coverage_total.info
3. genhtml coverage_total.info --branch-coverage --output-directory lcov

Expected behavior changes
no impact to behavior

System(s) tested on
OS: Ubuntu 18.04

Contributor Info - All information REQUIRED for consideration of pull request
Haven Carlson - NASA

[skliper]

Update the .github/workflows/unit-test-coverage.yml to match the updated coverage