Code coverage

Bun's test runner now supports built-in code coverage reporting. This makes it easy to see how much of the codebase is covered by tests, and find areas that are not currently well-tested.

Enabling coverage

bun:test supports seeing which lines of code are covered by tests. To use this feature, pass --coverage to the CLI. It will print out a coverage report to the console:

$ bun test --coverage
-------------|---------|---------|-------------------
File         | % Funcs | % Lines | Uncovered Line #s
-------------|---------|---------|-------------------
All files    |   38.89 |   42.11 |
 index-0.ts  |   33.33 |   36.84 | 10-15,19-24
 index-1.ts  |   33.33 |   36.84 | 10-15,19-24
 index-10.ts |   33.33 |   36.84 | 10-15,19-24
 index-2.ts  |   33.33 |   36.84 | 10-15,19-24
 index-3.ts  |   33.33 |   36.84 | 10-15,19-24
 index-4.ts  |   33.33 |   36.84 | 10-15,19-24
 index-5.ts  |   33.33 |   36.84 | 10-15,19-24
 index-6.ts  |   33.33 |   36.84 | 10-15,19-24
 index-7.ts  |   33.33 |   36.84 | 10-15,19-24
 index-8.ts  |   33.33 |   36.84 | 10-15,19-24
 index-9.ts  |   33.33 |   36.84 | 10-15,19-24
 index.ts    |  100.00 |  100.00 |
-------------|---------|---------|-------------------

To always enable coverage reporting by default, add the following line to your bunfig.toml:

[test]

# always enable coverage
coverage = true

By default coverage reports will include test files and exclude sourcemaps. This is usually what you want, but it can be configured otherwise in bunfig.toml.

[test]
coverageSkipTestFiles = true       # default false

Coverage thresholds

It is possible to specify a coverage threshold in bunfig.toml. If your test suite does not meet or exceed this threshold, bun test will exit with a non-zero exit code to indicate the failure.

[test]

# to require 90% line-level and function-level coverage
coverageThreshold = 0.9

# to set different thresholds for lines and functions
coverageThreshold = { lines = 0.9, functions = 0.9 }

Sourcemaps

Internally, Bun transpiles all files by default, so Bun automatically generates an internal source map that maps lines of your original source code onto Bun's internal representation. If for any reason you want to disable this, set test.coverageIgnoreSourcemaps to true; this will rarely be desirable outside of advanced use cases.

[test]
coverageIgnoreSourcemaps = true   # default false

Coverage reporters

By default, coverage reports will be printed to the console.

For persistent code coverage reports in CI environments and for other tools, you can pass a --coverage-reporter=lcov CLI option or coverageReporter option in bunfig.toml.

[test]
coverageReporter  = ["text", "lcov"]  # default ["text"]
coverageDir = "path/to/somewhere"  # default "coverage"

Reporter	Description
text	Prints a text summary of the coverage to the console.
lcov	Save coverage in lcov format.

lcov coverage reporter

To generate an lcov report, you can use the lcov reporter. This will generate an lcov.info file in the coverage directory.

[test]
coverageReporter = "lcov"