test_runner: avoid error when coverage line not found

lib/internal/test_runner/coverage.js

@@ -177,7 +177,7 @@ class TestCoverage {
           if (isBlockCoverage) {
             ArrayPrototypePush(branchReports, {
               __proto__: null,
-              line: range.lines[0].line,
+              line: range.lines[0]?.line,
               count: range.count,
             });
 
@@ -197,7 +197,7 @@ class TestCoverage {
             __proto__: null,
             name: functions[j].functionName,
             count: maxCountPerFunction,
-            line: range.lines[0].line,
+            line: range.lines[0]?.line,
           });
 
           if (range.count !== 0 || range.ignoredLines === range.lines.length) {

test/fixtures/test-runner/coverage-loader/hooks.mjs

@@ -0,0 +1,11 @@
+const source = `
+  import { test } from 'node:test';
+  test('test', async () => {});
+`;
+
+export async function load(url, context, nextLoad) {
+  if (url.endsWith('virtual.js')) {
+    return { format: "module", source, shortCircuit: true };
+  }
+  return nextLoad(url, context);
+}

test/fixtures/test-runner/coverage-loader/register-hooks.js

@@ -0,0 +1,4 @@
+const { register } = require('node:module');
+const { pathToFileURL } = require('node:url');
+
+register('./hooks.mjs', pathToFileURL(__filename));

test/parallel/test-runner-coverage.js

@@ -273,3 +273,33 @@ test('coverage with source maps', skipIfNoInspector, () => {
   assert(result.stdout.toString().includes(report));
   assert.strictEqual(result.status, 1);
 });
+
+test('coverage with ESM hook - source irrelevant', skipIfNoInspector, () => {
+  let report = [
+    '# start of coverage report',
+    '# ------------------------------------------------------------------',
+    '# file              | line % | branch % | funcs % | uncovered lines',
+    '# ------------------------------------------------------------------',
+    '# hooks.mjs         | 100.00 |   100.00 |  100.00 | ',
+    '# register-hooks.js | 100.00 |   100.00 |  100.00 | ',
+    '# virtual.js        | 100.00 |   100.00 |  100.00 | ',
+    '# ------------------------------------------------------------------',
+    '# all files         | 100.00 |   100.00 |  100.00 |',
+    '# ------------------------------------------------------------------',
+    '# end of coverage report',
+  ].join('\n');
+
+  if (common.isWindows) {
+    report = report.replaceAll('/', '\\');
+  }
+
+  const fixture = fixtures.path('test-runner', 'coverage-loader');
+  const args = [
+    '--import', './register-hooks.js', '--test', '--experimental-test-coverage', '--test-reporter', 'tap', 'virtual.js',
+  ];
+  const result = spawnSync(process.execPath, args, { cwd: fixture });
+
+  assert.strictEqual(result.stderr.toString(), '');
+  assert(result.stdout.toString().includes(report));
+  assert.strictEqual(result.status, 0);
+});