diff --git a/packages/@vue/cli/lib/__tests__/options.js b/packages/@vue/cli/lib/__tests__/options.js
index db01ce0d5..40e549559 100644
--- a/packages/@vue/cli/lib/__tests__/options.js
+++ b/packages/@vue/cli/lib/__tests__/options.js
@@ -1,5 +1,66 @@
 jest.mock('fs')
 
-it('should pass', () => {
+const fs = require('fs')
+const {
+  rcPath,
+  saveOptions,
+  loadSavedOptions,
+  savePartialOptions
+} = require('../options')
 
+it('save options', () => {
+  saveOptions({
+    packageManager: 'npm',
+    plugins: {},
+    foo: 'bar'
+  })
+  const options = JSON.parse(fs.readFileSync(rcPath, 'utf-8'))
+  expect(options).toEqual({
+    packageManager: 'npm',
+    plugins: {}
+  })
+})
+
+it('load options', () => {
+  expect(loadSavedOptions()).toEqual({
+    packageManager: 'npm',
+    plugins: {}
+  })
+  fs.unlinkSync(rcPath)
+  expect(loadSavedOptions()).toEqual({})
+})
+
+it('save partial options', () => {
+  savePartialOptions({
+    packageManager: 'yarn'
+  })
+  expect(loadSavedOptions()).toEqual({
+    packageManager: 'yarn'
+  })
+
+  savePartialOptions({
+    plugins: {
+      foo: { a: 1, b: 2 }
+    }
+  })
+  expect(loadSavedOptions()).toEqual({
+    packageManager: 'yarn',
+    plugins: {
+      foo: { a: 1, b: 2 }
+    }
+  })
+
+  savePartialOptions({
+    plugins: {
+      foo: { a: 2, c: 3 },
+      bar: { d: 4 }
+    }
+  })
+  expect(loadSavedOptions()).toEqual({
+    packageManager: 'yarn',
+    plugins: {
+      foo: { a: 2, b: 2, c: 3 },
+      bar: { d: 4 }
+    }
+  })
 })
diff --git a/packages/@vue/cli/lib/options.js b/packages/@vue/cli/lib/options.js
index 9dc93c7a5..3c935e6b8 100644
--- a/packages/@vue/cli/lib/options.js
+++ b/packages/@vue/cli/lib/options.js
@@ -64,7 +64,7 @@ const isObject = val => val && typeof val === 'object'
 function deepMerge (to, from) {
   for (const key in from) {
     if (isObject(to[key]) && isObject(from[key])) {
-      to[key] = deepMerge(to[key], from[key])
+      deepMerge(to[key], from[key])
     } else {
       to[key] = from[key]
     }