Bun Test Coverage
Bun has built-in code coverage reporting without additional dependencies.
Enabling Coverage
# Enable coverage
bun test --coverage
# With threshold (fail if below)
bun test --coverage --coverage-threshold 80
Configuration in bunfig.toml
[test]
coverage = true
coverageThreshold = 0.8 # 80% minimum
coverageDir = "./coverage"
# Patterns to ignore
coverageSkipTestFiles = true
Coverage Output
------------------|---------|---------|-------------------
File | % Funcs | % Lines | Uncovered Line #s
------------------|---------|---------|-------------------
All files | 85.71 | 89.23 |
src/index.ts | 100.00 | 100.00 |
src/utils.ts | 75.00 | 82.35 | 23-25, 41-43
src/api.ts | 80.00 | 85.00 | 67, 89-92
------------------|---------|---------|-------------------
Coverage Reporters
# Default console output
bun test --coverage
# Generate lcov report
bun test --coverage --coverage-reporter=lcov
# Multiple reporters
bun test --coverage --coverage-reporter=text --coverage-reporter=lcov
Available Reporters
| Reporter | Output |
|---|---|
text |
Console table (default) |
lcov |
coverage/lcov.info for CI tools |
json |
coverage/coverage.json |
Coverage Thresholds
Set minimum coverage requirements:
# Fail if coverage < 80%
bun test --coverage --coverage-threshold 80
# Per-metric thresholds in bunfig.toml
[test]
coverage = true
coverageThreshold = {
lines = 80,
functions = 75,
branches = 70
}
Excluding Files
[test]
coverage = true
# Skip test files from coverage
coverageSkipTestFiles = true
# Patterns to exclude
coverageIgnore = [
"**/*.test.ts",
"**/fixtures/**",
"**/mocks/**"
]
CI Integration
GitHub Actions
- name: Run tests with coverage
run: bun test --coverage --coverage-reporter=lcov
- name: Upload coverage to Codecov
uses: codecov/codecov-action@v5
with:
files: ./coverage/lcov.info
Output Directory
# Custom output directory
bun test --coverage --coverage-dir=./reports/coverage
Programmatic Coverage
import { test, expect } from "bun:test";
// Get coverage data programmatically
const coverage = Bun.coverage;
// Access after tests complete
process.on("exit", () => {
console.log(coverage.getCoverageData());
});
Common Errors
| Error | Cause | Fix |
|---|---|---|
Coverage threshold not met |
Coverage below threshold | Increase test coverage |
No coverage data |
Files not executed | Check test includes file |
lcov not found |
Missing reporter | Add --coverage-reporter=lcov |
Best Practices
- Set realistic thresholds - Start at 60%, increase gradually
- Exclude generated files - Mock files, type definitions
- Focus on critical paths - Business logic over boilerplate
- Run in CI - Prevent coverage regression
When to Load References
Load references/reporters.md when:
- Custom reporter configuration
- CI/CD integration details
- Codecov/Coveralls setup
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