Add additional StyleSheet tests for styled-components

Author: kitten

src/__tests__/visitor.test.js

@@ -31,6 +31,10 @@ const {
   ReactCurrentDispatcher
 } = (React: any).__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED
 
+const {
+  StyleSheet
+} = require('styled-components').__DO_NOT_USE_OR_YOU_WILL_BE_HAUNTED_BY_SPOOKY_GHOSTS
+
 let prevDispatcher = null
 
 beforeEach(() => {
@@ -48,6 +52,10 @@ afterEach(() => {
 const Noop = () => null
 
 describe('visitElement', () => {
+  beforeEach(() => {
+    StyleSheet.reset(true)
+  })
+
   it('walks Fragments', () => {
     const element = (
       <Fragment>
@@ -115,14 +123,32 @@ describe('visitElement', () => {
       [],
       () => {}
     )
+
     expect(children.length).toBe(1)
     expect(children[0].type).toBe(Noop)
+    expect(StyleSheet.master.tags.length).toBe(1)
+
+    const tag = StyleSheet.master.tags[0]
+    expect(tag.css().trim()).toBe('')
+
+    expect(Object.keys(StyleSheet.master.deferred)).toEqual([
+      expect.any(String)
+    ])
   })
 
   it('walks StyledComponent wrapper elements', () => {
     const Comp = styled(Noop)``
     const children = visitElement(<Comp />, [], () => {})
+
     expect(children.length).toBe(1)
+    expect(StyleSheet.master.tags.length).toBe(1)
+
+    const tag = StyleSheet.master.tags[0]
+    expect(tag.css().trim()).toBe('')
+
+    expect(Object.keys(StyleSheet.master.deferred)).toEqual([
+      expect.any(String)
+    ])
   })
 
   it('walks Providers and Consumers', () => {