test_runner: fix coverage ignore comments to exclude BRDA entries

When using /* node:coverage ignore next */ comments, the test_runner
correctly excluded DA (line coverage) entries from lcov output, but
still included BRDA (branch coverage) entries as uncovered. This caused
branch coverage to report lower percentages than expected.

This fix ensures that branches completely covered by ignore comments
are excluded from the branch coverage report, matching the behavior
of c8 and user expectations.

Fixes: #61586

Author: wdsmini

lib/internal/test_runner/coverage.js

@@ -193,18 +193,23 @@ class TestCoverage {
           ObjectAssign(range, mapRangeToLines(range, lines));
 
           if (isBlockCoverage) {
-            ArrayPrototypePush(branchReports, {
-              __proto__: null,
-              line: range.lines[0]?.line,
-              count: range.count,
-            });
-
-            if (range.count !== 0 ||
-                range.ignoredLines === range.lines.length) {
+            // Skip branches that are completely ignored
+            if (range.ignoredLines === range.lines.length) {
+              totalBranches++;
               branchesCovered++;
+            } else {
+              ArrayPrototypePush(branchReports, {
+                __proto__: null,
+                line: range.lines[0]?.line,
+                count: range.count,
+              });
+
+              if (range.count !== 0) {
+                branchesCovered++;
+              }
+
+              totalBranches++;
             }
-
-            totalBranches++;
           }
         }
 

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

@@ -0,0 +1,13 @@
+// Test fixture for issue #61586
+// Tests that node:coverage ignore next also excludes BRDA entries
+
+function getValue(condition) {
+  if (condition) {
+    return 'truthy';
+  }
+  /* node:coverage ignore next */
+  return 'falsy';
+}
+
+// Call only the truthy branch
+getValue(true);

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

@@ -0,0 +1,43 @@
+'use strict';
+const common = require('../common');
+const assert = require('node:assert');
+const { spawnSync } = require('node:child_process');
+const { test } = require('node:test');
+const fixtures = require('../common/fixtures');
+const skipIfNoInspector = {
+  skip: !process.features.inspector ? 'inspector disabled' : false
+};
+
+test('coverage ignore next excludes BRDA for ignored branches', skipIfNoInspector, async (t) => {
+  const fixture = fixtures.path('test-runner', 'coverage-ignore-branch.js');
+  const args = [
+    '--experimental-test-coverage',
+    '--test-reporter', 'lcov',
+    fixture,
+  ];
+  const result = spawnSync(process.execPath, args);
+  const lcovOutput = result.stdout.toString();
+
+  // Parse the LCOV output
+  const lines = lcovOutput.split('\n');
+  const brdaLines = lines.filter(l => l.startsWith('BRDA:'));
+
+  // All branches should be covered (no uncovered branches)
+  // The branch leading to the ignored code should be excluded
+  const uncoveredBranches = brdaLines.filter(l => l.endsWith(',0'));
+
+  assert.strictEqual(uncoveredBranches.length, 0,
+    `Expected no uncovered branches, but found: ${uncoveredBranches.join(', ')}`);
+
+  // Verify branch coverage is 100%
+  const brfLine = lines.find(l => l.startsWith('BRF:'));
+  const brhLine = lines.find(l => l.startsWith('BRH:'));
+  assert(brfLine, 'Should have BRF line');
+  assert(brhLine, 'Should have BRH line');
+
+  const brf = parseInt(brfLine.split(':')[1], 10);
+  const brh = parseInt(brhLine.split(':')[1], 10);
+
+  assert.strictEqual(brf, brh,
+    `Expected branch coverage to be 100% (${brh}/${brf}), but found ${brh}/${brf}`);
+});