Legacy Code Refactoring

Coverage is very useful when you refactor legacy C++ code and want to understand which code paths your current tests exercise.

The Challenge

Legacy code refactoring is risky:

Limited or no tests exist
Original developers are gone
Documentation is outdated
Behavior is poorly understood

Coverage as a Safety Net

Code coverage helps de-risk refactoring:

Measure baseline – See what existing tests cover
Identify gaps – Find untested high-risk areas
Add tests first – Build safety net before changes
Refactor with confidence – Tests catch regressions
Verify coverage maintained – Ensure nothing is broken

Baseline coverage

Run your existing tests under covdbg and store a baseline database:

covdbg --output "C:\path\to\baseline.covdb" "C:\path\to\existing_tests.exe"Code language: PowerShell (powershell)

Export the baseline for reporting:

covdbg convert --input "C:\path\to\baseline.covdb" --format LCOV --output "C:\path\to\baseline.lcov"Code language: PowerShell (powershell)

Focus on the module you want to change

Put include/exclude filters into .covdbg.yaml so covdbg only tracks the module you are working on:

version: 1
source_root: "."
coverage:
  default:
    files:
      include:
        - "legacy_module/**"
      exclude:
        - "build/**"Code language: YAML (yaml)

Then run:

covdbg --config ".covdbg.yaml" --output "focused.covdb" "tests.exe"Code language: PowerShell (powershell)

Incremental Testing Strategy

Step 1: Establish Baseline

Run existing tests and record coverage:

covdbg --output "baseline.covdb" "existing_tests.exe"
covdbg convert -i baseline.covdb -f LCOV -o baseline.lcovCode language: PowerShell (powershell)

Step 2: Identify Critical Gaps

Export to LCOV and use coverage tools (e.g., lcov-viewer, genhtml) to find:

Functions with 0% coverage (high risk)
Complex functions with partial coverage
Error handling paths never tested

Step 3: Add Tests Incrementally

Write tests for uncovered areas, re-run coverage:

# After adding new tests
covdbg --output "with_new_tests.covdb" "tests.exe"

# Compare coverage improvement
covdbg convert -i with_new_tests.covdb -f LCOV -o improved.lcovCode language: PowerShell (powershell)

Step 4: Refactor with Confidence

With adequate coverage in place:

Make small, focused changes
Re-run tests to catch regressions
Verify coverage remains stable or improves

Combining Multiple Test Types

Merge unit tests and manual testing coverage:

# Unit tests
covdbg --output "unit.covdb" "unit_tests.exe"

# Integration/manual tests
covdbg --output "integration.covdb" "app.exe"

# Merge for complete picture
covdbg merge -i unit.covdb -i integration.covdb -o combined.covdbCode language: PowerShell (powershell)