Add end 2 end test to category addition (#13102)

This commit adds end 2 end tests to the category addition. Taxonomies are an area of the editor where we had some regressions in the past.
This is just a start, more tests will be added to test complex interactions using custom taxonomies.

test/e2e/specs/taxonomies.test.js

@@ -0,0 +1,96 @@
+/**
+ * Internal dependencies
+ */
+import {
+	findSidebarPanelWithTitle,
+	newPost,
+	openDocumentSettingsSidebar,
+	publishPost,
+} from '../support/utils';
+
+describe( 'Taxonomies', () => {
+	const canCreatTermInTaxonomy = ( taxonomy ) => {
+		return page.evaluate(
+			( _taxonomy ) => {
+				const post = wp.data.select( 'core/editor' ).getCurrentPost();
+				if ( ! post._links ) {
+					return false;
+				}
+				return !! post._links[ `wp:action-create-${ _taxonomy }` ];
+			},
+			taxonomy
+		);
+	};
+
+	const getSelectCategories = () => {
+		return page.evaluate(
+			() => {
+				return Array.from( document.querySelectorAll(
+					'.editor-post-taxonomies__hierarchical-terms-input:checked'
+				) ).map( ( node ) => {
+					return node.parentElement.querySelector(
+						'label'
+					).innerText;
+				} );
+			}
+		);
+	};
+
+	it( 'should be able to open the categories panel and create a new main category if the user has the right capabilities', async () => {
+		await newPost();
+
+		await openDocumentSettingsSidebar();
+
+		const categoriesPanel = await findSidebarPanelWithTitle( 'Categories' );
+		expect( categoriesPanel ).toBeDefined();
+
+		// Open the categories panel.
+		await categoriesPanel.click( 'button' );
+
+		// If the user has no permission to add a new category finish the test.
+		if ( ! ( await canCreatTermInTaxonomy( 'category' ) ) ) {
+			return;
+		}
+
+		await page.waitForSelector( 'button.editor-post-taxonomies__hierarchical-terms-add' );
+
+		// Click add new category button.
+		await page.click( 'button.editor-post-taxonomies__hierarchical-terms-add' );
+
+		// Type the category name in the field.
+		await page.type(
+			'.editor-post-taxonomies__hierarchical-terms-input[type=text]',
+			'z rand category 1'
+		);
+
+		// Click the submit button.
+		await page.click( '.editor-post-taxonomies__hierarchical-terms-submit' );
+
+		// Wait for the categories to load.
+		await page.waitForSelector( '.editor-post-taxonomies__hierarchical-terms-input:checked' );
+
+		let selectedCategories = await getSelectCategories();
+
+		// The new category is selected.
+		expect( selectedCategories ).toHaveLength( 1 );
+		expect( selectedCategories[ 0 ] ).toEqual( 'z rand category 1' );
+
+		// Type something in the title so we can publish the post.
+		await page.type( '.editor-post-title__input', 'Hello World' );
+
+		// Publish the post.
+		await publishPost();
+
+		// Reload the editor.
+		await page.reload();
+
+		// Wait for the categories to load.
+		await page.waitForSelector( '.editor-post-taxonomies__hierarchical-terms-input:checked' );
+
+		selectedCategories = await getSelectCategories();
+
+		// The category selection was persisted after the publish process.
+		expect( selectedCategories ).toHaveLength( 1 );
+		expect( selectedCategories[ 0 ] ).toEqual( 'z rand category 1' );
+	} );
+} );