feat(functional components): add context to all functional components (#126)

* closes #117

* remove brackets

* add test case

Author: rssfrncs

src/lib/create-instance.js

@@ -11,23 +11,29 @@ import { throwError } from './util'
 import cloneDeep from 'lodash/cloneDeep'
 import { compileTemplate } from './compile-template'
 
-export default function createConstructor (component: Component, options: Options): Component {
+export default function createConstructor (
+  component: Component,
+  options: Options
+): Component {
   const vue = options.localVue || Vue
 
-  if (options.context) {
-    if (!component.functional) {
-      throwError('mount.context can only be used when mounting a functional component')
-    }
-
-    if (typeof options.context !== 'object') {
+  if (component.functional) {
+    if (options.context && typeof options.context !== 'object') {
       throwError('mount.context must be an object')
     }
     const clonedComponent = cloneDeep(component)
     component = {
       render (h) {
-        return h(clonedComponent, options.context)
+        return h(
+          clonedComponent,
+          options.context || component.FunctionalRenderContext
+        )
       }
     }
+  } else if (options.context) {
+    throwError(
+      'mount.context can only be used when mounting a functional component'
+    )
   }
 
   if (options.provide) {

test/unit/specs/mount/options/context.spec.js

@@ -49,4 +49,20 @@ describe('context', () => {
     const fn = () => mount(Component, { context })
     expect(fn).to.throw().with.property('message', message)
   })
+
+  it('mounts functional component with a defined context when no context object passed in options', () => {
+    const defaultValue = '[vue-test-utils]: testProp default value'
+    const Component = {
+      functional: true,
+      props: {
+        testProp: {
+          type: String,
+          default: defaultValue
+        }
+      },
+      render: (h, { props }) => h('div', props.testProp)
+    }
+    const wrapper = mount(Component)
+    expect(wrapper.element.textContent).to.equal(defaultValue)
+  })
 })