[WIP] Network emulation for Chrome

[EtienneBruines]

• Closes Simulate offline mode #235

User facing changelog

• Added new command cy.network() that simulates network conditions

Additional details

This allows you to simulate network conditions, such as being offline or on a slow 3G network.

How has the user experience changed?

It allows the following:

    cy.contains('We are currently online.')
    cy.network({ offline: true })
    cy.contains('We are currently offline.')
    cy.network({ offline: false })
    cy.contains('We are currently online.')

PR Tasks

• Have tests been added/updated?
• Has the original issue been tagged with a release in ZenHub?
• Has a PR for user-facing changes been opened in cypress-documentation?
• Have API changes been updated in the type definitions?
• Have new configuration options been added to the cypress.schema.json? not applicable
• Does it work in Chrome?
• Does it work in Electron?
• Does it work in Firefox? Yes, but:
  • Implement Network.emulateNetworkConditions in Firefox
  • Enable CDP for Firefox
    • Bump Browser.getVersion to 1.3 in Firefox
    • Support Network.getAllCookies in Firefox
  • Handle older Firefox versions (by throwing a useful error explaining cy.network not being available)
• Makes service-workers behave like they're offline
  • A test has been written to confirm this behavior
• cy.request should be unaffected
  • A test has been written to confirm this behavior

[cypress-bot]

Thanks for the contribution! Below are some guidelines Cypress uses when doing PR reviews.

• Please write [WIP] in the title of your Pull Request if your PR is not ready for review - someone will review your PR as soon as the [WIP] is removed.
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PR Review Checklist

If any of the following requirements can't be met, leave a comment in the review selecting 'Request changes', otherwise 'Approve'.

User Experience

• The feature/bugfix is self-documenting from within the product.
• The change provides the end user with a way to fix their problem (no dead ends).

Functionality

• The code works and performs its intended function with the correct logic.
• Performance has been factored in (for example, the code cleans up after itself to not cause memory leaks).
• The code guards against edge cases and invalid input and has tests to cover it.

Maintainability

• The code is readable (too many nested 'if's are a bad sign).
• Names used for variables, methods, etc, clearly describe their function.
• The code is easy to understood and there are relevant comments explaining.
• New algorithms are documented in the code with link(s) to external docs (flowcharts, w3c, chrome, firefox).
• There are comments containing link(s) to the addressed issue (in tests and code).

Quality

• The change does not reimplement code.
• There's not a module from the ecosystem that should be used instead.
• There is no redundant or duplicate code.
• There are no irrelevant comments left in the code.
• Tests are testing the code’s intended functionality in the best way possible.

Internal

• The original issue has been tagged with a release in ZenHub.

[CLAassistant]

All committers have signed the CLA.

[flotwig]

Thanks for opening a PR! This is a good idea, but I think it is better suited to be used as a separate NPM module users can require in their support file for now.

While this is definitely functionality we eventually want to have in Cypress core, the lack of Firefox support blocks this from being merged for now.

---

Handles cy.request
- No idea what the desired behavior is here?

cy.request is simply a means for the user to perform a normal, unintercepted HTTP request from their test code, so it should be exempt from any network conditioning that applies to their test code.

[EtienneBruines]

Thank you @flotwig for your reply.

For supporting Firefox, we should be able to simulate clicks towards the user-facing "Work offline" function of Firefox.

As far as I know, the cy.click() command clicks within the app, is there a way to emulate clicks on the browser window itself? e.g. such that we can enable/disable Work offline?

That would go a long way in bridging the gap until Firefox offers "real" API-support for it.

Because lack of Firefox-support seems like the only major blocking issue, this would seem like a doable workaround - one that I can imagine people will be happy with.

(Whether released in the end as separate package or as PR - I don't mind either way. I would like to offer as much functionality as possible on this topic.)

[jennifer-shehane]

is there a way to emulate clicks on the browser window itself? e.g. such that we can enable/disable Work offline

@EtienneBruines no, there's no way to do this currently, you'd have to work through Firefox's available APIs to enable/disable work offline mode.

When you do publish a plugin, you can open a pull request to add it to our documentation? Instructions here.

Closing this PR for now.