test_runner: account for newline in source maps

This commit updates the source mapping logic in the test runner
to account for newline characters that are not included in line
length calculations.

Co-authored-by: Simon Chan <[email protected]>
Fixes: #54240

lib/internal/test_runner/coverage.js

@@ -340,8 +340,8 @@ class TestCoverage {
       const { data, lineLengths } = sourceMapCache[url];
       let offset = 0;
       const executedLines = ArrayPrototypeMap(lineLengths, (length, i) => {
-        const coverageLine = new CoverageLine(i + 1, offset, null, length);
-        offset += length;
+        const coverageLine = new CoverageLine(i + 1, offset, null, length + 1);
+        offset += length + 1;
         return coverageLine;
       });
       if (data.sourcesContent != null) {

test/fixtures/test-runner/source-map-line-lengths/index.ts

@@ -0,0 +1,76 @@
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+1;
+function a() {
+  console.log(1);
+}
+a();

test/parallel/test-runner-coverage.js

@@ -428,3 +428,16 @@ test('coverage with included and excluded files', skipIfNoInspector, () => {
   assert.strictEqual(result.status, 0);
   assert(!findCoverageFileForPid(result.pid));
 });
+
+test('properly accounts for line endings in source maps', skipIfNoInspector, () => {
+  const fixture = fixtures.path('test-runner', 'source-map-line-lengths', 'index.js');
+  const args = [
+    '--test', '--experimental-test-coverage', '--test-reporter', 'tap',
+    fixture,
+  ];
+  const result = spawnSync(process.execPath, args);
+  const report = 'index.ts | 100.00 |   100.00 |  100.00 |';
+  assert.strictEqual(result.stderr.toString(), '');
+  assert(result.stdout.toString().includes(report));
+  assert.strictEqual(result.status, 0);
+});