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Bun’s test runner has built-in code coverage reporting. Enable it with the --coverage flag.
terminal
bun test --coverage

test.test.ts:
✓ math > add [0.71ms]
✓ math > multiply [0.03ms]
✓ random [0.13ms]
-------------|---------|---------|-------------------
File         | % Funcs | % Lines | Uncovered Line #s
-------------|---------|---------|-------------------
All files    |   66.67 |   77.78 |
 math.ts     |   50.00 |   66.67 |
 random.ts   |   50.00 |   66.67 |
-------------|---------|---------|-------------------

 3 pass
 0 fail
 3 expect() calls
To set a minimum coverage threshold, add the following to your bunfig.toml. A threshold of 0.9 requires that tests cover 90% of your codebase.
bunfig.toml
[test]
# to require 90% line-level and function-level coverage
coverageThreshold = 0.9
If your test suite does not meet this threshold, bun test exits with a non-zero exit code to signal a failure.
terminal
bun test --coverage

<test output>
$ echo $?
1 # this is the exit code of the previous command
You can set different thresholds for line-level and function-level coverage.
bunfig.toml
[test]
# to set different thresholds for lines and functions
coverageThreshold = { lines = 0.5, functions = 0.7 }
See Code coverage.