test_runner: fix coverage function call counts

lib/internal/test_runner/coverage.js

@@ -263,10 +263,8 @@ class TestCoverage {
       for (let j = 0; j < functions.length; ++j) {
         const { isBlockCoverage, ranges } = functions[j];
 
-        let maxCountPerFunction = 0;
         for (let k = 0; k < ranges.length; ++k) {
           const range = ranges[k];
-          maxCountPerFunction = MathMax(maxCountPerFunction, range.count);
 
           // Add some useful data to the range. The test runner has read these ranges
           // from a file, so we own the data structures and can do what we want.
@@ -294,7 +292,7 @@ class TestCoverage {
           ArrayPrototypePush(functionReports, {
             __proto__: null,
             name: functions[j].functionName,
-            count: maxCountPerFunction,
+            count: range.count,
             line: range.lines[0]?.line,
           });
 

test/fixtures/test-runner/coverage-function-count.js

@@ -0,0 +1,15 @@
+'use strict';
+const assert = require('node:assert');
+const { test } = require('node:test');
+
+function sum(n) {
+  let result = 0;
+  for (let i = 0; i < n; i++) {
+    result += i;
+  }
+  return result;
+}
+
+test('sum', () => {
+  assert.strictEqual(sum(10), 45);
+});

test/parallel/test-runner-coverage-function-count.js

@@ -0,0 +1,40 @@
+'use strict';
+const common = require('../common');
+common.skipIfInspectorDisabled();
+
+// Loop iterations must not inflate function call counts.
+const assert = require('node:assert');
+const { spawnSync } = require('node:child_process');
+const fixtures = require('../common/fixtures');
+
+const fixture = fixtures.path('test-runner', 'coverage-function-count.js');
+const jsonReporter = fixtures.fileURL('test-runner/custom_reporters/coverage.mjs');
+
+for (const isolation of ['process', 'none']) {
+  for (const reporter of [jsonReporter, 'lcov']) {
+    const { status, signal, stdout, stderr } = spawnSync(process.execPath, [
+      '--test',
+      '--experimental-test-coverage',
+      `--test-isolation=${isolation}`,
+      '--test-coverage-exclude=!test/**',
+      `--test-coverage-include=${fixture}`,
+      '--test-reporter', reporter,
+      fixture,
+    ], { encoding: 'utf8' });
+
+    assert.strictEqual(status, 0, stderr);
+    assert.strictEqual(signal, null);
+    assert.strictEqual(stderr, '');
+
+    if (reporter === 'lcov') {
+      assert.match(stdout, /^FNDA:1,sum$/m);
+    } else {
+      const { summary: { files } } = JSON.parse(stdout);
+      assert.strictEqual(files.length, 1);
+      const [file] = files;
+      assert.strictEqual(file.functions.find((fn) => fn.name === 'sum').count, 1);
+      assert.strictEqual(file.lines.find((line) => line.line === 8).count, 10);
+      assert(file.branches.some((branch) => branch.count === 10));
+    }
+  }
+}