test_runner: mark ignored branches as covered in coverage report

lib/internal/test_runner/coverage.js

@@ -263,7 +263,7 @@ class TestCoverage {
             ArrayPrototypePush(branchReports, {
               __proto__: null,
               line: range.lines[0]?.line,
-              count: range.count,
+              count: range.ignoredLines === range.lines.length ? 1 : range.count,
             });
 
             if (range.count !== 0 ||

test/fixtures/test-runner/coverage-ignore-branch.js

@@ -0,0 +1,11 @@
+'use strict';
+
+function getValue(condition) {
+  if (condition) {
+    return 'truthy';
+  }
+  /* node:coverage ignore next */
+  return 'falsy';
+}
+
+module.exports = { getValue };

test/fixtures/test-runner/coverage-ignore-branch.test.js

@@ -0,0 +1,10 @@
+'use strict';
+const { describe, it } = require('node:test');
+const assert = require('node:assert');
+const { getValue } = require('./coverage-ignore-branch.js');
+
+describe('getValue', () => {
+  it('should return truthy when condition is true', () => {
+    assert.strictEqual(getValue(true), 'truthy');
+  });
+});

test/parallel/test-runner-coverage.js

@@ -566,3 +566,28 @@ test('coverage with directory and file named "file"', skipIfNoInspector, () => {
   assert.strictEqual(result.status, 0);
   assert(result.stdout.toString().includes('start of coverage report'));
 });
+
+// Regression test for https://github.com/nodejs/node/issues/61586
+// When a branch leads to ignored code, it should be marked as covered.
+test('coverage ignores branches leading to ignored code', skipIfNoInspector, async (t) => {
+  const fixture = fixtures.path('test-runner', 'coverage-ignore-branch.test.js');
+  const child = spawnSync(process.execPath,
+                          [
+                            '--test',
+                            '--experimental-test-coverage',
+                            '--test-coverage-exclude=!test/**',
+                            '--test-reporter',
+                            fixtures.fileURL('test-runner/custom_reporters/coverage.mjs'),
+                            fixture,
+                          ]);
+  assert.strictEqual(child.stderr.toString(), '');
+  const stdout = child.stdout.toString();
+  const coverage = JSON.parse(stdout);
+
+  const file = coverage.summary.files.find((f) => f.path.endsWith('coverage-ignore-branch.js'));
+  assert(file, 'Expected coverage-ignore-branch.js in coverage report');
+
+  // All branches should be covered because the untaken falsy branch
+  // leads to code that is ignored via /* node:coverage ignore next */.
+  assert.strictEqual(file.coveredBranchCount, file.totalBranchCount);
+});