BREAKING CHANGE: Use cy.task for health check rather than cy.exec

This will fix #104 (and hopefully #138).

`cy.task` will always execute within the version of node that is bundled with
Cypress, so we no longer have to worry about `$PATH` issues that `cy.exec`
faces. We're also no longer running a CLI command for the health check, this new
implementation will make a HTTP request from node.

This does mean we need to update the docs to let users know there's an extra
step to configure the SDK properly now.

In an ideal world we would be able to `.catch` on `cy.request` and disable Percy
after the first failed `POST` of the DOM. I think in the future we should look
into working with Cypress to implement this so we can shrink the integration,
make the SDK more reliable, and faster (since we won't make 2 network requests
per-snapshot).

.gitignore

@@ -1,2 +1,3 @@
 node_modules/
 dist/
+cypress/screenshots

cypress/plugins/index.js

@@ -10,17 +10,19 @@
 
 // This function is called when a project is opened or re-opened (e.g. due to
 // the project's config changing)
+const percyHealthCheck = require("../../dist/task");
 
 module.exports = (on, config) => {
   // `on` is used to hook into various events Cypress emits
   // `config` is the resolved Cypress config
 
   // Make it possible to log things to stdout by calling 'cy.task('log', 'some message to log').
   // Useful for development and debugging.
-  on('task', {
-    log (message) {
-      console.log(message)
-      return null
+  on("task", {
+    log(message) {
+      console.log(message);
+      return null;
     }
-  })
-}
+  });
+  on("task", percyHealthCheck);
+};

lib/index.ts

@@ -5,43 +5,33 @@ declare const Cypress: any
 declare const cy: any
 
 Cypress.Commands.add('percySnapshot', (name: string, options: any = {}) => {
-  const percyAgentClient = new PercyAgent({
-    handleAgentCommunication: false,
-    domTransformation: options.domTransformation
-  })
-
-  // Use cy.exec(...) to check if percy agent is running. Ideally this would be
-  // done using something like cy.request(...), but that's not currently possible,
-  // for details, see: https://github.com/cypress-io/cypress/issues/3161
-  const healthcheckCmd = `percy health-check -p ${percyAgentClient.port}`
-  cy.exec(healthcheckCmd, { failOnNonZeroExit: false }).then(({ stderr }: any) => {
-    if (stderr) {
-      // Percy server not available
-      cy.log('[percy] Percy agent is not running. Skipping snapshots')
-      cy.log(stderr)
-
-      return
-    }
+  cy.task('percyHealthCheck').then((percyIsRunning: boolean) => {
+    if (percyIsRunning) {
+      const percyAgentClient = new PercyAgent({
+        handleAgentCommunication: false,
+        domTransformation: options.domTransformation
+      })
 
-    name = name || cy.state('runnable').fullTitle()
+      name = name || cy.state('runnable').fullTitle()
 
-    cy.document().then((doc: Document) => {
-      options.document = doc
-      const domSnapshot = percyAgentClient.snapshot(name, options)
-      return cy.request({
-        method: 'POST',
-        url: `http://localhost:${percyAgentClient.port}/percy/snapshot`,
-        failOnStatusCode: false,
-        body: {
-          name,
-          url: doc.URL,
-          enableJavaScript: options.enableJavaScript,
-          widths: options.widths,
-          clientInfo: clientInfo(),
-          environmentInfo: environmentInfo(),
-          domSnapshot
-        }
+      cy.document().then((doc: Document) => {
+        options.document = doc
+        const domSnapshot = percyAgentClient.snapshot(name, options)
+        return cy.request({
+          method: 'POST',
+          url: `http://localhost:${percyAgentClient.port}/percy/snapshot`,
+          failOnStatusCode: false,
+          body: {
+            name,
+            url: doc.URL,
+            enableJavaScript: options.enableJavaScript,
+            widths: options.widths,
+            clientInfo: clientInfo(),
+            environmentInfo: environmentInfo(),
+            domSnapshot
+          }
+        })
       })
-    })
+    }
   })
 })

lib/task.ts

@@ -0,0 +1,8 @@
+import Axios from 'axios'
+
+export function percyHealthCheck() {
+  return Axios
+    .get('http://localhost:5338/percy/healthcheck')
+    .then(() =>  true)
+    .catch(() =>  false)
+}

package.json

@@ -41,7 +41,8 @@
     "typescript": "^3.0.3"
   },
   "dependencies": {
-    "@percy/agent": "~0"
+    "@percy/agent": "~0",
+    "axios": "^0.18.1"
   },
   "release": {
     "plugins": [