diff --git a/spec/main-process/atom-application.test.js b/spec/main-process/atom-application.test.js
index b73a57fab..8d991f52c 100644
--- a/spec/main-process/atom-application.test.js
+++ b/spec/main-process/atom-application.test.js
@@ -389,6 +389,34 @@ describe('AtomApplication', function () {
       assert.deepEqual(app2Window.representedDirectoryPaths, [])
     })
 
+    describe('when the `pidToKillWhenClosed` flag is passed', () => {
+      let killedPids, atomApplication
+
+      beforeEach(() => {
+        killedPids = []
+        atomApplication = buildAtomApplication({
+          killProcess (pid) { killedPids.push(pid) }
+        })
+      })
+
+      it('kills the specified pid after a newly-opened window is closed', async () => {
+        const window1 = atomApplication.launch(parseCommandLine([makeTempDir(), '--wait', '--pid', '101']))
+        await focusWindow(window1)
+
+        const [window2] = atomApplication.launch(parseCommandLine(['--wait', '--pid', '102']))
+        await focusWindow(window2)
+        assert.deepEqual(killedPids, [])
+
+        window1.close()
+        await window1.closedPromise
+        assert.deepEqual(killedPids, [101])
+
+        window2.close()
+        await window2.closedPromise
+        assert.deepEqual(killedPids, [101, 102])
+      })
+    })
+
     describe('when closing the last window', () => {
       if (process.platform === 'linux' || process.platform === 'win32') {
         it('quits the application', async () => {
@@ -529,11 +557,11 @@ describe('AtomApplication', function () {
     assert(electron.app.didQuit())
   })
 
-  function buildAtomApplication () {
-    const atomApplication = new AtomApplication({
+  function buildAtomApplication (params = {}) {
+    const atomApplication = new AtomApplication(Object.assign({
       resourcePath: ATOM_RESOURCE_PATH,
-      atomHomeDirPath: process.env.ATOM_HOME
-    })
+      atomHomeDirPath: process.env.ATOM_HOME,
+    }, params))
     atomApplicationsToDestroy.push(atomApplication)
     return atomApplication
   }
diff --git a/src/main-process/atom-application.js b/src/main-process/atom-application.js
index 459520722..df5c5e202 100644
--- a/src/main-process/atom-application.js
+++ b/src/main-process/atom-application.js
@@ -101,6 +101,7 @@ class AtomApplication extends EventEmitter {
     this.socketPath = options.socketPath
     this.logFile = options.logFile
     this.userDataDir = options.userDataDir
+    this._killProcess = options.killProcess || process.kill.bind(process)
     if (options.test || options.benchmark || options.benchmarkTest) this.socketPath = null
 
     this.pidsToOpenWindows = {}
@@ -880,7 +881,7 @@ class AtomApplication extends EventEmitter {
   killProcess (pid) {
     try {
       const parsedPid = parseInt(pid)
-      if (isFinite(parsedPid)) process.kill(parsedPid)
+      if (isFinite(parsedPid)) this._killProcess(parsedPid)
     } catch (error) {
       if (error.code !== 'ESRCH') {
         console.log(`Killing process ${pid} failed: ${error.code != null ? error.code : error.message}`)