add heading tests

docs/src/demos/Extensions/Heading/index.spec.js

@@ -1,5 +1,31 @@
 context('/api/extensions/heading', () => {
   beforeEach(() => {
     cy.visit('/api/extensions/heading')
+
+    cy.get('.ProseMirror').window().then(window => {
+      const { editor } = window
+      editor.setContent('<p>Example Text</p>')
+      editor.focus().selectAll()
+    })
+  })
+
+  describe('blockquote', () => {
+    it('the button should make the selected line a h1', () => {
+      cy.get('.ProseMirror h1').should('not.exist')
+      cy.get('.demo__preview button:nth-child(1)').click({ force: true })
+      cy.get('.ProseMirror').contains('h1', 'Example Text')
+    })
+
+    it('the button should make the selected line a h2', () => {
+      cy.get('.ProseMirror h2').should('not.exist')
+      cy.get('.demo__preview button:nth-child(2)').click({ force: true })
+      cy.get('.ProseMirror').contains('h2', 'Example Text')
+    })
+
+    it('the button should make the selected line a h3', () => {
+      cy.get('.ProseMirror h3').should('not.exist')
+      cy.get('.demo__preview button:nth-child(3)').click({ force: true })
+      cy.get('.ProseMirror').contains('h3', 'Example Text')
+    })
   })
 })