Can Cypress Mock Internal Variable Value Inside Function In Runtime Like Jest Does?

Cypress and Jest serve different purposes:

• Jest is a unit testing framework that allows mocking functions, modules, and variables at runtime.
• Cypress is an end-to-end testing framework that runs in a browser, which makes it difficult to mock internal variables in runtime like Jest does.

Can Cypress mock internal variables inside a function at runtime?

No, Cypress cannot mock internal variables inside a function at runtime like Jest. It runs in a browser and lacks Jest’s runtime control.

Alternatives in Cypress

1. Stub Functions (cy.stub()) – If the function is accessible on window

cy.window().then((win) => {
  cy.stub(win, 'getActionTypeName').returns('RUNTIME_RESET_TYPE');
});

2. Dependency Injection – Refactor the function to accept dependencies

export const functionBeingTested = (getActionTypeName) => {
  return getActionTypeName();
};

Then in your Cypress test:

cy.wrap(() => 'RUNTIME_RESET_TYPE').as('mockFn');
cy.get('@mockFn').then((mockFn) => {
  expect(functionBeingTested(mockFn)).to.eq('RUNTIME_RESET_TYPE');
});

3. Intercept API Calls (cy.intercept()) – Mock API responses:

cy.intercept('GET', '/api/action-type', { actionType: 'RUNTIME_RESET_TYPE' });

4. Use Environment Variables – Control behavior via Cypress config

Cypress.env('ACTION_TYPE', 'RUNTIME_RESET_TYPE');

Then in your app:

const actionType = Cypress.env('ACTION_TYPE') || getActionTypeName();

Conclusion

While Cypress can’t mock internal variables like Jest, it offers workarounds through stubbing, dependency injection, API interception, and environment variables.

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