fix: allow using findComponent on a functional component (#1593)

Author: dobromir-hristov

packages/test-utils/src/wrapper.js

@@ -237,7 +237,7 @@ export default class Wrapper implements BaseWrapper {
    */
   findComponent(rawSelector: Selector): Wrapper | ErrorWrapper {
     const selector = getSelector(rawSelector, 'findComponent')
-    if (!this.vm) {
+    if (!this.vm && !this.isFunctionalComponent) {
       throwError(
         'You cannot chain findComponent off a DOM element. It can only be used on Vue Components.'
       )

test/specs/wrapper/find.spec.js

@@ -162,6 +162,18 @@ describeWithShallowAndMount('find', mountingMethod => {
       .with.property('message', message)
   })
 
+  it('allows using findComponent on functional component', () => {
+    const FuncComponentWithChildren = {
+      functional: true,
+      components: {
+        ChildComponent: Component
+      },
+      render: h => h('div', {}, [h(Component)])
+    }
+    const wrapper = mountingMethod(FuncComponentWithChildren)
+    expect(wrapper.findComponent(Component).exists()).to.be.true
+  })
+
   itSkipIf(isRunningPhantomJS, 'returns Wrapper of class component', () => {
     const TestComponent = {
       template: `