add blockquote extension with documentation, demo and tests

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

@@ -0,0 +1,48 @@
+context('/api/extensions/blockquote', () => {
+  beforeEach(() => {
+    cy.visit('/api/extensions/blockquote')
+
+    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 blockquote', () => {
+      cy.get('.demo__preview button:first').click({ force: true })
+      cy.get('.ProseMirror').contains('blockquote', 'Example Text')
+    })
+
+    it('the button should toggle the blockquote', () => {
+      cy.get('.demo__preview button:first').click({ force: true })
+      cy.get('.ProseMirror').contains('blockquote', 'Example Text')
+      cy.get('.demo__preview button:first').click({ force: true })
+      cy.get('.ProseMirror blockquote').should('not.exist')
+    })
+
+    it('the keyboard shortcut should make the selected line a blockquote', () => {
+      cy.get('.ProseMirror').type('{meta}{shift}9', {force: true})
+      cy.get('.ProseMirror').contains('blockquote', 'Example Text')
+    })
+
+    it('the keyboard shortcut should toggle the blockquote', () => {
+      cy.get('.ProseMirror').type('{meta}{shift}9', {force: true})
+      cy.get('.ProseMirror').contains('blockquote', 'Example Text')
+      cy.get('.ProseMirror').type('{meta}{shift}9', {force: true})
+      cy.get('.ProseMirror blockquote').should('not.exist')
+    })
+
+    it('should make a blockquote form markdown shortcuts', () => {
+      cy.get('.ProseMirror').window().then(window => {
+        const { editor } = window
+        editor.clearContent()
+
+        cy.get('.ProseMirror')
+          .type('> Quote', {force: true})
+          .contains('blockquote', 'Quote')
+      })
+    })
+  })
+})