chore(test): scenario for checking socket message order

test/e2e/communications.feature

@@ -0,0 +1,19 @@
+Feature: Client-Server Communications
+  In order to use Karma
+  As a person who wants to write great tests
+  I want to be able to run tests from the command line.
+
+  Scenario: Messages arrive in order
+    Given a configuration with:
+      """
+      files = ['communications/test.js'];
+      browsers = ['ChromeHeadlessNoSandbox'];
+      plugins = [
+        'karma-jasmine',
+        'karma-chrome-launcher'
+      ];
+      """
+    And the environment:
+      | DEBUG | * |
+    When I start Karma
+    Then the stderr contains in order socket.io logs

test/e2e/step_definitions/core_steps.js

@@ -17,6 +17,13 @@ Given('a proxy on port {int} that prepends {string} to the base path', async fun
   return this.proxy.start(proxyPort, proxyPath)
 })
 
+Given('the environment:', function (env) {
+  this.env = {}
+  for (const [key, value] of env.rawTable) {
+    this.env[key] = value
+  }
+})
+
 When('I stop a server programmatically', function (callback) {
   setTimeout(() => {
     stopper.stop(this.config, (exitCode) => {
@@ -149,3 +156,22 @@ Then(/^the file at ([a-zA-Z0-9/\\_.]+) contains:$/, function (filePath, expected
     throw new Error('Expected output to match the following:\n  ' + expectedOutput + '\nGot:\n  ' + data)
   }
 })
+
+Then('the stderr contains in order socket.io logs', function (callback) {
+  const regex = /emitting event (.*)/g
+  const found = Array.from(this.lastRun.stderr.matchAll(regex))
+  const events = []
+  // eslint-disable-next-line no-unused-vars
+  for (const [_, group] of found) {
+    events.push(JSON.parse(group))
+  }
+  const eventSequence = ['register', 'start', 'result', 'complete']
+  for (let i = 0; i < eventSequence.length; i++) {
+    const expectedEvent = eventSequence[i]
+    const actualEvent = events[i][0]
+    if (actualEvent !== expectedEvent) {
+      throw new Error(`Expected event '${expectedEvent}' at position ${i}, but got '${actualEvent}' instead`)
+    }
+  }
+  callback()
+})

test/e2e/support/communications/test.js

@@ -0,0 +1,5 @@
+describe('a suite', function () {
+  it('a spec', function () {
+    expect().nothing()
+  })
+})

test/e2e/support/world.js

@@ -149,7 +149,7 @@ module.exports = (config) => {
 
   async runForegroundProcess (args) {
     return new Promise((resolve) => {
-      exec(`${this.karmaExecutable} ${args}`, { cwd: this.workDir }, (error, stdout, stderr) => {
+      exec(`${this.karmaExecutable} ${args}`, { cwd: this.workDir, env: { ...process.env, ...this.env } }, (error, stdout, stderr) => {
         this.lastRun.error = error
         this.lastRun.stdout = stdout.toString()
         this.lastRun.stderr = stderr.toString()