# Which test covers this line? Per-test coverage in Vitest

> Vitest reports coverage for the whole run, not per test. Supercov runs your Vitest command and shows which tests cover any line, and what each test covers.

Web page: https://supercov.com/compare/vitest-per-test-coverage · Published 2026-10-01
All Supercov pages for agents: https://supercov.com/llms.txt · Full text: https://supercov.com/llms-full.txt

## Which test covers this line?

Vitest's coverage report shows which lines ran during the whole run, not which
test ran them. Supercov runs your Vitest command and records coverage for each
test, so one run answers both questions: which tests cover this line, and what
does this test cover.

```sh
npx supercov -- npx vitest run
npx supercov runs latest line src/price.js:7
```

```text
src/price.js:7

Source
      7 | return subtotal - 10;

Covering tests
  takes 10 off orders over 100 [vitest:604050779_1] — unit/vitest
```

Recorded on October 1, 2026 with Supercov 2.0.1 and Vitest 5.0.0. The output is
shortened; the full example is below.

## The example

One function and three tests in two files:

```js
// src/price.js
export function price(items, coupon) {
  const subtotal = items.reduce((sum, item) => sum + item.price * item.qty, 0);
  if (coupon === 'HALF') {
    return subtotal / 2;
  }
  if (subtotal > 100) {
    return subtotal - 10;
  }
  return subtotal;
}
```

```js
// tests/cart.test.js
test('sums the cart', () => {
  expect(price([{ price: 20, qty: 2 }])).toBe(40);
});

test('takes 10 off orders over 100', () => {
  expect(price([{ price: 60, qty: 2 }])).toBe(110);
});

// tests/coupon.test.js
test('HALF halves the total', () => {
  expect(price([{ price: 30, qty: 2 }], 'HALF')).toBe(30);
});
```

## What Vitest shows on its own

Vitest's V8 and Istanbul [coverage providers](https://vitest.dev/guide/coverage)
report one result for the run. To see what a single test covers, filter the run
to it:

```sh
npx vitest run --coverage -t "takes 10 off orders over 100"
```

```text
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
 price.js |   71.42 |       50 |     100 |   66.66 | 4,9
```

That answers "what does this test cover?" for one test. To find every test that
covers line 7, you would run each test this way and compare the reports.

## Every test that covers a line

```sh
npx supercov runs latest line src/price.js:2
```

```text
Covering tests
  HALF halves the total [vitest:1298185237_0] — unit/vitest
  sums the cart [vitest:604050779_0] — unit/vitest
  takes 10 off orders over 100 [vitest:604050779_1] — unit/vitest
```

All three tests compute the subtotal. Line 4 is covered by `HALF halves the
total` alone, so it is the test to read before you change the coupon rule.

## Everything one test covers

```sh
npx supercov runs latest test "takes 10 off orders over 100"
```

```text
takes 10 off orders over 100
outcome passed; retry 0=passed
5 lines, 6 hits, 2 decisions, 1 phases
line: src/price.js:1
line: src/price.js:2
line: src/price.js:3
line: src/price.js:6
line: src/price.js:7
assertion: expect.toBe at tests/cart.test.js:9:3
```

It also names the assertion the test made. Add `--json` to any query for
structured output a coding agent can read.

## Limits

Supercov attributes coverage to each Vitest test exactly, with setup code kept
separate and Browser Mode included; see [runner
support](https://supercov.com/docs/supported-suites.md). It runs your tests in an isolated copy and
does not change them. It does not replace Vitest's coverage report: use that
for the run's totals, and Supercov when you need to know which test is
responsible for a line. For V8 versus Istanbul, see [Vitest coverage: V8 vs
Istanbul](https://supercov.com/compare/vitest-coverage.md).