test(cypress-github-backend): optionally record tests and run using recorded data (#2776)

cypress/Readme.md

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+# Cypress Tests Guide
+
+## Introduction
+
+[Cypress](https://www.cypress.io/) is a JavaScript End to End Testing Framework that runs in the browser.
+
+Cypress tests run with a [local version](../dev-test) of the CMS.
+
+During the setup of a spec file, the relevant `index.html` and `config.yml` are copied from `dev-test/backends/<backend>` to `dev-test`.
+
+Tests for the `test` backend use mock data generated in `dev-test/backends/test/index.html`.
+
+Tests for the `github` backend use previously [recorded data](fixtures) and stub `fetch` [calls](support/commands.js#L82). See more about recording tests data [here](#recording-tests-data).
+
+## Run Tests Locally
+
+```bash
+yarn test:e2e # builds the demo site and runs Cypress in headless mode with mock data
+```
+
+## Debug Tests
+
+```bash
+yarn develop # starts a local dev server with the demo site
+yarn test:e2e:exec # runs Cypress in non-headless mode with mock data
+```
+
+## Recording Tests Data
+
+> Currently only relevant for `github` backend tests.
+
+When recording tests, access to the GitHub API is required, thus one must set up a `.env` file in the root project directory in the following format:
+
+```bash
+GITHUB_REPO_OWNER=owner
+GITHUB_REPO_NAME=repo
+GITHUB_REPO_TOKEN=tokenWithWritePermissions
+GITHUB_OPEN_AUTHORING_OWNER=forkOwner
+GITHUB_OPEN_AUTHORING_TOKEN=tokenWithWritePermissions
+```
+
+> The structure of the repo designated by `GITHUB_REPO_OWNER/GITHUB_REPO_NAME` should match the settings in [`config.yml`](../dev-test/backends/github/config.yml#L1)
+
+To start a recording run the following commands:
+
+```bash
+yarn develop # starts a local dev server with the demo site
+yarn mock:server:start # starts the recording proxy
+yarn test:e2e:record-fixtures:dev # runs Cypress in non-headless and pass data through the recording proxy
+yarn mock:server:stop # stops the recording proxy
+```
+
+> During the recorded process a clone of `GITHUB_REPO_NAME` will be created under `.temp` and reset between tests.
+
+Recordings are sanitized from any possible sensitive data and [transformed](plugins/github.js#L395) into an easier to process format.
+
+To avoid recording all the tests over and over again, a recommended process is to:
+
+1. Mark the specific test as `only` by changing `it("some test...` to `it.only("some test...` for the relevant test.
+2. Run the test in recording mode.
+3. Exit Cypress and stop the proxy.
+4. Run the test normally (with mock data) to verify the recording works.
+
+## Debugging Playback Failures
+
+Most common failures are:
+
+1. The [recorded data](utils/mock-server.js#L17) is not [transformed](plugins/github.js#L395) properly (e.g. [sanitization](plugins/github.js#L283) broke something).
+2. The [stubbed requests and responses](support/commands.js#L82) are not [matched](support/commands.js#L29) properly (e.g. timestamp changes in request body between recording and playback).
+
+Dumping all recorded data as is to a file [here](utils/mock-server.js#L24) and adding a `debugger;` statement [here](support/commands.js#L52) is useful to gain insights.
+
+Also comparing console log messages between recording and playback is very useful (ordering of requests, etc.)