--experimental-test-coverage throws TypeError if directory is named file

[joshuaavalon]

Version

24.12.0

Platform

Microsoft Windows NT 10.0.22631.0 x64

Subsystem

test_runner

What steps will reproduce the bug?

Run test node test with --experimental-test-coverage on source code with a directory named file.

Steps to Reproduce

1. Create src/file/index.js

export function a() {
 console.log("!");
 return 1;
}

2. Create src/file/__tests__/index.spec.js

import { describe, it } from "node:test";
import assert from "node:assert/strict";
import { a } from "../index.js"

describe("a", async function () {
 it("test", async function () {
 const result = a();
 assert.equal(result, 1);
 })
});

3. npm run test with node --experimental-test-coverage --test \"./src/**/__tests__/*.{spec,test}.js\".

Findings

node/lib/internal/test_runner/utils.js

Lines 552 to 555 in dcb9573

	function printCoverageBodyTree(tree, depth = 0) {
	for (const key in tree) {
	if (tree[key].file) {
	const file = tree[key].file;

In printCoverageBodyTree, a directory named file seems to conflict with internal variable named file. Causing it to treat the directory as a file.

How often does it reproduce? Is there a required condition?

100%

What is the expected behavior? Why is that the expected behavior?

Generate test coverage normally.

What do you see instead?

TypeError: String.prototype.split called on null or undefined
 at split (<anonymous>)
 at printCoverageBodyTree (node:internal/test_runner/utils:536:44)
 at printCoverageBodyTree (node:internal/test_runner/utils:565:9)
 at getCoverageReport (node:internal/test_runner/utils:585:3)
 at #handleEvent (node:internal/test_runner/reporter/spec:102:16)
 at SpecReporter._transform (node:internal/test_runner/reporter/spec:112:37)
 at Transform._write (node:internal/streams/transform:171:8)
 at writeOrBuffer (node:internal/streams/writable:570:12)
 at _write (node:internal/streams/writable:499:10)
 at Writable.write (node:internal/streams/writable:508:10)
Emitted 'error' event on Readable instance at:
 at emitErrorNT (node:internal/streams/destroy:170:8)
 at emitErrorCloseNT (node:internal/streams/destroy:129:3)
 at process.processTicksAndRejections (node:internal/process/task_queues:90:21)

Additional information

No response

[Han5991]

I think it only works on Windows

[joshuaavalon]

@Han5991 I pretty sure it works on Linux because I first found it out on GitHub action.
I created a repository. https://github.com/joshuaavalon/node-coverage

https://github.com/joshuaavalon/node-coverage/actions/runs/20357487020/job/58495852805

[Han5991]

It works on Mac too!