test_runner: node:coverage ignore comments exclude DA but leave BRDA in lcov output

Version

v24.13.0

Platform

Darwin 24.6.0 (macOS)

Subsystem

test_runner

What steps will reproduce the bug?

1. Create a file with a branch and /* node:coverage ignore next */ comment:

// src/example.js
function getValue(condition) {
  if (condition) {
    return 'truthy';
  }
  /* node:coverage ignore next */
  return 'falsy';
}

module.exports = { getValue };

2. Create a test that only covers the truthy branch:

// test/example.test.js
const { describe, it } = require('node:test');
const assert = require('node:assert');
const { getValue } = require('../src/example.js');

describe('getValue', () => {
  it('should return truthy when condition is true', () => {
    assert.strictEqual(getValue(true), 'truthy');
  });
});

3. Run with coverage:

node --experimental-test-coverage --test-reporter=lcov --test-reporter-destination=coverage/lcov.info --test test/example.test.js

4. Examine the generated lcov.info

How often does it reproduce? Is there a required condition?

Always reproducible.

What is the expected behavior? Why is that the expected behavior?

The /* node:coverage ignore next */ comment should exclude both:

• The DA (line coverage) entry for the ignored line
• The BRDA (branch coverage) entry for the branch leading to the ignored code

This is the expected behavior because:

1. The purpose of ignore comments is to exclude code from coverage calculations
2. c8 (which also uses V8 coverage) correctly handles this by marking both DA and BRDA as covered for ignored lines

What do you see instead?

• DA: Line 6 (return 'falsy';) is correctly excluded from the lcov output
• BRDA: Branch entry remains as uncovered: BRDA:4,2,0,0

BRDA:1,0,0,1
BRDA:1,1,0,1
BRDA:4,2,0,0    <-- This branch should be excluded but remains as uncovered
BRF:3
BRH:2           <-- Only 2 of 3 branches hit (66.67%)
DA:1,1
DA:2,1
DA:3,1
DA:4,1
DA:5,0
DA:7,1          <-- DA:6 is missing (correctly excluded)
...

This causes branch coverage to report 66.67% instead of 100%, which impacts CI/CD pipelines that enforce branch coverage thresholds.

Additional information

Comparison with c8:

Using c8 with /* c8 ignore next */ on the same code structure produces the correct result:

DA:5,1          # Line marked as covered (ignored)
DA:6,1          # Line marked as covered (ignored)
BRDA:5,2,0,1    # Branch marked as covered (ignored)
BRF:3
BRH:3           # All 3 branches "hit" (100%)

Minimal reproduction repository:

https://github.com/tobigumo/node-coverage-brda-bug

git clone https://github.com/tobigumo/node-coverage-brda-bug.git
cd node-coverage-brda-bug
npm install
npm run test
# Compare coverage/lcov-native.info (Node.js native - has bug) with coverage/lcov.info (c8 - correct)

从最小复现仓库开始，运行其原生 coverage 命令和 c8 coverage 命令，对比 coverage/lcov-native.info 与 coverage/lcov.info。跟踪 test_runner 对 example.js 的 ignore 注释和 test/example.test.js 案例的 coverage 与 lcov 处理。完成的标准是，被忽略的分支不再产生未覆盖的 BRDA 条目，并且分支覆盖率报告为 100%。