cypress-clojurescript-preprocessor

A Cypress preprocessor for ClojureScript, which uses Shadow CLJS for processing Cypress tests written in ClojureScript.

The plugin works by inspecting the Cypress integrationFolder (by default, cypress/integration) for ClojureScript files (*.cljs, e.g. cypress/integration/my_app/app_test.cljs -> (ns my-app.app-test)) and generates a shadow-cljs.edn configuration file with a build for each test file. This configuration is then used to compile the tests into Javascript before submitting to the browser.

The shadow-cljs server is kept running while the Cypress runner is active. When a test is run, the test file is watched for changes and a recompile is done if the test file is changed and Cypress is notified to rerun the test. The first compile is a bit slow, but subsequent compiles are fast (the plugin uses shadow-cljs compile command, which defaults to optimizations: none).

Rationale: Should you use this?

I think a small word of warning should be in order if you intend to use this plugin :) I had a great time hacking this together over a period of time, but maxed out at getting a REPL flow working, which I think makes the current implementation quite complex, since Cypress isn't quite REPL friendly (check out the issue on REPL support). Also, I haven't updated the plugin to work with latest Cypress versions, which has changed the preprocessor API, so I don't think the current latest versio of this preprocessor works with current latest Cypress.

There's good reading on rationale in #12 and possible future directions in #16, so I suggesst checking them out. If you are still interested, continue reading :)

Example usage

1. Create a project

   $ mkdir cypress-cljs-sample
   $ cd cypress-cljs-sample
   $ echo {} > package.json

2. Install Cypress

   npm install cypress --save-dev

3. Install cypress-clojurescript-preprocessor

   npm install cypress-clojurescript-preprocessor

4. Configure ClojureScript preprocessor

   $ mkdir -p cypress/plugins
   $ cat << EOF > cypress/plugins/index.js
   const makeCljsPreprocessor = require('cypress-clojurescript-preprocessor');
   /**
    * @type {Cypress.PluginConfig}
    */
   module.exports = (on, config) => {
     on('file:preprocessor', makeCljsPreprocessor(config));
   };
   EOF

   This will delegate files other than *.cljs to the default Browserify preprocessor. If you need to run other preprocessors, then combine them with for example:

   module.exports = (on, config) => {
     const browserifyPreprocessor = makeBrowserifyPreprocessor();
     const cljsPreprocessor = makeCljsPreprocessor(config);
     // Use the default Browserify preprocessor for files other than *.cljs
     on('file:preprocessor', (file) => file.filePath.endsWith('.cljs') ? cljsPreprocessor(file) : browserifyPreprocessor(file));
   };

5. Write test in ClojureScript

   $ mkdir -p cypress/integration/examples
   $ cat << EOF > cypress/integration/examples/window.cljs
   (ns examples.window
     (:require-macros [latte.core :refer [describe beforeEach it]]))
   
   (def cy js/cy)
   
   (describe "Window"
     (beforeEach []
       (.visit cy "https://example.cypress.io/commands/window"))
     (it "cy.window() - get the global window object" []
       (.should (.window cy) "have.property" "top")))
   EOF

6. Run test

   ./node_modules/.bin/cypress open

REPL in Cypress

You can active REPL into a test in the browser that Cypress is controlling.

1. Lookup NREPL port used by the shadow-cljs server

   $ cat .preprocessor-cljs/.shadow-cljs/nrepl.port
   50796
   

2. Connect to the NREPL server and list builds

   shadow.user> (shadow/get-build-ids)
   (:npm :local :window_foo :window)
   

3. Open a test in the Cypress runner

4. Start shadow-cljs watch on the test that is open in the Cypress runner

   shadow.user> (shadow/watch :window)
   [:window] Configuring build.
   [:window] Compiling ...
   [:window] Build completed. (119 files, 0 compiled, 0 warnings, 1.22s)
   :watching
   

   The build-id is a keyword of the test file name

5. Start a ClojureScript repl

   shadow.user> (shadow/repl :window)
   To quit, type: :cljs/quit
   [:selected :window]
   cljs.user> (js/alert "plop") ;; To try out that it works
   

Now you can use the slightly undocumented now command to execute Cypress command immediately, for example, to select an option:

cljs.user> (-> (.now js/cy "get" "#some-opt")
               (.then (fn [el]
                        (.now js/cy "select" el "two"))))
#object[Promise [object Promise]]

6. When done, exit the repl and stop shadow-cljs watch for the repl build

   cljs.user> :cljs/quit
   Exited CLJS session. You are now in CLJ again.
   :cljs/quit
   shadow.user> 
   (shadow/stop-worker :window)
   Worker shutdown.
   :stopped
   

Some references to the now command:

• cypress-io/cypress#6080 (comment)
• https://docs.cypress.io/guides/guides/debugging#Run-Cypress-command-outside-the-test
• cypress-io/cypress#8195
• cypress-io/cypress#3636 (comment)

Configuration

Shadow CLJS configuration override

The Shadow CLJS configuration used by the preprocessor may be overridden via a shadow-cljs-override.edn file, which is merged on top of the default configuration with meta-merge. By default, [mocha-latte "0.1.2"] and [chai-latte "0.2.0"] are included in the shadow-cljs.edn configuration used by the preprocessor.

Shared namespaces

The working directory of the shadow-cljs compiler that is driven by the preprocessor is the cypress folder. Because of this, in order to include shared code that is in a folder at the same level as the cypress directory, use a relative (or absolute path) e.g.

$ tree -I "node_modules" -P common.cljs\|window.cljs
.
├── cypress
│   ├── fixtures
│   ├── integration
│   │   └── examples
│   │       └── window.cljs
│   ├── plugins
│   └── support
└── src ;; shared code directory
    └── net
        └── tiuhti
            └── common.cljs
$ cat shadow-cljs-override.edn
{:source-paths ["../src"]} ;; path relative to `cypress` directory
$ head -3 cypress/integration/examples/window.cljs
(ns examples.window
  (:require-macros [latte.core :refer [describe beforeEach it]])
  (:require [net.tiuhti.common :as common]))  ;; require namespace in the `src` directory

Dependencies used by the shared code would have to be specified in the :dependencies key in shadow-cljs-override.edn file.

Development

Here's some notes on how to develop this library.

Shadow-cljs repl

The preprocessor is written in ClojureScript and compiled to a npm library with the help of shadow-cljs. To develop the library in a ClojureScript repl:

1. Start node repl via shadow-cljs node-repl
2. Connect to the nrepl server for example from Emacs with cider: cider-connect
3. In nrepl at the shadow.user> prompt, switch to the node repl via: (shadow/repl :node-repl)

Use locally compiled version

To use a local version of the preprocessor, point the client project to the local clone of the preprocessor:

{
  "devDependencies": {
    "cypress": "^7.6.0",
    "shadow-cljs": "^2.14.5"      ;; <-- Also, need to have shadow-cljs installed in the client project
  },
  "dependencies": {
    "cypress-clojurescript-preprocessor": "../cypress-clojurescript-preprocessor"  ;;  <-- Directory of the local copy
  }
}

Note the the client project also needs shadow-cljs to be installed (apparently :)).

Then, compile your changes via

$ npm run prepare

And (re)start Cypress in the client project:

$ ./node_modules/.bin/cypress open

Changelog

• 0.2.0
  • Support REPL in an open test, allows to use the "now" command
  • Finally fix zombie processes after exit, by using signal-exit, thanks to this blog post
  • Detech shadow-cljs startup by polling port/pid files and remove race condition around subprocess stdout/stderr
• 0.1.7
  • Bump shadow-cljs to 2.14.5
  • Call process/exit to not leave zombies when Cypress exits
  • When adding a new test while the preprocessor is running
    • Use same optimization level as for initial build config
    • Prevent duplicate merge of shadow-cljs-override.edn
• 0.1.6 Support namespaces with multiple segments (thanks @martinklepsch !), also files with underscore. Bump chokidar to 3.5.2
• 0.1.5 Merge override config ontop final config, allows to add additional :source-paths
• 0.1.4 Bundle browserify preprocessor
• 0.1.3 Add shadow-cljs-override.edn
• 0.1.2 Bundle Bundle mocha-latte and chai-latte
• 0.1.0 Initial release