stryker-js: Frequent timeouts when running tests with Stryker

Summary

When Running Stryker I frequently see a score of 100% because of tests timing out. This not consitent and varies greatly between runs. The timeouts occur very frequent on a larger TypeScript React project but can also be repeated frequently on a small project.

Note that there is one empty test here and all that is needed to reproduce this is an import of a very simple React component.

The test file:

import Label from "./Label";

test("dummy", () => {});

The Label.tsx being imported:

import React, { ReactElement, ReactChild } from "react";

type LabelProps = {
  caption: ReactChild;
  name?: string;
};

const Label = ({ caption, name }: LabelProps): ReactElement => {
  return <label htmlFor={name}>{caption}</label>;
};

Label.displayName = "Label";

export default Label;

The initial test run always passed but then subsequent mutation runs sometimes fail with a timeout. These timeouts appear to occur about 20% of the time in the small sample project but are a lot more frequent on a large project. The timeouts in the small project always seem to be either 0, 2 or 4, there are a total of 4 mutant generated. I have seen a run with either 1 or 3 timeouts.

I have uploaded the sample project to a GitHub repository here

Stryker config

// This config was generated using a preset.
// Please see the handbook for more information: https://github.com/stryker-mutator/stryker-handbook/blob/master/stryker/guides/react.md#react
module.exports = function(config) {
  config.set({
    mutate: [
      "src/**/*.ts?(x)",
      "!src/*.ts?(x)",
      "!src/**/*@(.test|.spec|Spec).ts?(x)"
    ],
    mutator: "typescript",
    testRunner: "jest",
    reporters: ["progress", "clear-text", "html"],
    coverageAnalysis: "off",
    tempDirName: "stryker-tmp",
    jest: {
      projectType: "react"
    }
  });
};

Test runner config

Jest with the standard Create-React-App configuration.

Stryker environment

stryker-test@0.1.0 C:\Temp\stryker-test
+-- @stryker-mutator/core@2.3.0
| +-- @stryker-mutator/api@2.3.0
| +-- @stryker-mutator/util@2.3.0
+-- @stryker-mutator/html-reporter@2.3.0
| +-- @stryker-mutator/api@2.3.0 deduped
| +-- @stryker-mutator/util@2.3.0 deduped
+-- @stryker-mutator/jest-runner@2.3.0
| +-- @stryker-mutator/api@2.3.0 deduped
+-- @stryker-mutator/typescript@2.3.0
| +-- @stryker-mutator/api@2.3.0 deduped
| +-- @stryker-mutator/util@2.3.0 deduped

"react-scripts": "3.2.0"
jest@24.9.0

Test runner environment

# Test command
yarn test
"test": "react-scripts test",

Your Environment

software	version(s)
node	v10.15.3
npm	6.11.3
Operating System	Windows 10 version 1809

Add stryker.log

stryker.log