Unit test runs very slow (6 sec per a test)

• Issue

After config ts-jest to create-react app successfully, I saw a test case run 6s. That’s very slow. My jest config following the document: (ts|tsx)": “<rootDir>/node_modules/ts-jest/preprocessor.js”

My code

describe("App", () => {
    it("renders only 1 App component", () => {
        const component = shallow(<App />);
        console.log(component.html())
        expect(component).toHaveLength(1);
    });
});

Result: PASS src/containers/test/App.spec.tsx (6.119s)

• Expected behavior

I searched some tutorials on the internet, there is a preprocessor.js file:

const tsc = require("typescript");
const tsConfig = require("./tsconfig.json");

module.exports = {
  process(src, path) {
    if (path.endsWith(".ts") || path.endsWith(".tsx")) {
      return tsc.transpile(src, tsConfig.compilerOptions, path, []);
    } else if (path.endsWith(".js") ) {
      return tsc.transpile(src, tsConfig.compilerOptions, path, []);
    }
    return src;
  }
};

If I use this file, the test case runs on 3 -4s. Can you explain me this problem? Does preprocessor.js of TS-Jest have more functionalities than that file as well?

[bbugh]

If you’re having trouble with this, you could try running jest with --maxWorkers=1 or --runInBand. We were having very slow tests too, but running it with only one worker (which is what both of those commands do) reduced our run time by 95% in a local dev test. Seems counter-intuitive, but it’s working. runInBand says it’s intended for debugging purposes, so I’d stick to the maxWorkers flag if it works for you.

[Loremaster]

@EvanDarwin I am experiencing issues with slow tests too. It can take around 30-50 seconds for a single test. Were you able to resolve it?