cy.exec timeout with backgrounded process

ghz 2days ago ⋅ 5 views

I'm trying to start a server using cy.execand background the process like so:

cy.exec('nohup python -m my_module arg_1 &', { failOnNonZeroExit: false }).then(result => {
    if (result.code != 0) {
      throw new Error(`Execution of "${command}" failed
      Exit code: ${result.code}
      Stdout:\n${result.stdout}
      Stderr:\n${result.stderr}`);
    }
  })

This, however, causes the timeout error as if the process was running in the foreground. I realize that starting the server with cy.exec is an antipattern but I have a very peculiar case where I need to start a server with different parameters for every test. I thought that by backgrounding the process I could circumvent the timeout requirement of cy.exec.

If that is not an option, though, what would be the best practice for this scenario i.e. starting a different server per cypress test?

Answer

Using cy.exec for backgrounding a process like you attempted is indeed an anti-pattern, as cy.exec waits for the process to finish, and starting it in the background doesn't fulfill this requirement.

The best practice for starting a server per Cypress test (with different parameters) would involve a few alternative approaches:

1. Use cy.task for Server Management

Instead of relying on cy.exec, you can use cy.task to run custom tasks that manage the server lifecycle outside of the Cypress test execution. This gives you more flexibility, as you can execute long-running background processes without blocking the test itself.

In your plugins/index.js:

module.exports = (on, config) => {
  on('task', {
    startServer({ arg1 }) {
      return new Promise((resolve, reject) => {
        const { exec } = require('child_process');
        exec(`nohup python -m my_module ${arg1} &`, (error, stdout, stderr) => {
          if (error) {
            reject(`Error starting server: ${stderr}`);
          } else {
            resolve(stdout);
          }
        });
      });
    }
  });
};

In your test file:

describe('Server Test', () => {
  it('starts a server with a unique argument', () => {
    cy.task('startServer', { arg1: 'some-arg' }).then(result => {
      console.log(result);
      // Continue with your tests
    });
  });
});

2. Use Fixtures for Server Setup

If the server setup can be handled before the test run (like once before all tests), you could use before or beforeEach hooks in combination with a cy.exec or cy.task to launch the server.

beforeEach(() => {
  cy.exec('nohup python -m my_module arg_1 &');
});

3. Use Docker Containers (For Complex Cases)

For complex setups where you need isolated environments or different servers for each test, you can use Docker containers. Docker's ability to manage different services with various configurations can be extremely useful in such cases. You can use cypress-docker to spin up and tear down containers during the test lifecycle.

4. Polling or Waiting for Server to be Ready

In some cases, if you must start the server using cy.exec and background it, you can add polling to check if the server is running by hitting an endpoint or checking for a process.

describe('Server Test', () => {
  it('starts a server and waits for it to be ready', () => {
    cy.exec('nohup python -m my_module arg_1 &');
    
    // Wait for the server to be ready (using a dummy URL or health check)
    cy.request('GET', 'http://localhost:your-port/status').its('status').should('eq', 200);

    // Continue with the tests
  });
});

Conclusion

Using cy.task for managing the server process outside the test execution is the most flexible approach. This way, the server runs in the background without affecting the Cypress test's flow.

#py