jamiemason Testing Gaps
Find untested branches and missing real-world test scenarios for a source file.
Workflow
- Run text coverage for the target file
- Identify uncovered branches from the output
- Cross-reference with test file to understand what's tested
- Report uncovered branches + missing real-world scenarios
Step 1: Run Coverage
Use cargo llvm-cov with --text output (not --html) for parseable results.
# Full coverage, filtered to target file
cargo llvm-cov test --text \
--ignore-run-fail \
--ignore-filename-regex '(_test.rs|\/test\/)' \
2>/dev/null | sed -n '/TARGET_FILE\.rs:/,/^$/p'
Example for preferred_semver.rs:
cargo llvm-cov test --text \
--ignore-run-fail \
--ignore-filename-regex '(_test.rs|\/test\/)' \
2>/dev/null | sed -n '/preferred_semver\.rs:/,/^$/p'
Step 2: Read Coverage Output
The text format shows per-line execution counts:
42| 80| .and_then(|range| ...) # Hit 80 times
74| 0| Some(preferred) # Never hit
321| 0| instance.mark_conflict(...) # Never hit
count > 0= coveredcount = 0= uncovered branch^Nannotations on sub-expressions show partial coverage within a line
Extract only uncovered lines
... | grep -E '^\s+\d+\|\s+0\|'
Step 3: Classify Gaps
For each uncovered branch, determine:
- What code path leads here? — Trace the
if/elsechain backward - What input would trigger it? — What package.json + config combination
- Is it reachable? — Some branches may be defensive/unreachable
- Is it worth testing? — Real-world scenario vs theoretical edge case
Categories
| Category | Action |
|---|---|
| Real-world scenario never tested | Write a test |
| Edge case in existing logic | Write a test |
| Defensive branch (unreachable) | Note but skip |
| Dead code | Consider removing |
Step 4: Identify Missing Scenarios
Beyond line coverage, look for missing combinations:
- Feature A tested, Feature B tested, A+B never tested together
- Only tested with one package, never with multiple
- Only tested with
highestSemver, neverlowestSemver - Only tested with one range type (
^), never others (>=,<=) - Only tested without semver groups, never with
Step 5: Report
Structure findings as:
- Uncovered branches — Specific lines, what triggers them, why untested
- Missing real-world scenarios — Combinations and interactions not covered
Running Tests After Adding Coverage
just test # All tests
cargo test test_name -- --nocapture # Specific test
just coverage # Regenerate coverage report