Add an e2e test for the autop issue

test/e2e/specs/__snapshots__/compatibility-classic-editor.test.js.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Compatibility with Classic Editor Should not apply autop when rendering blocks 1`] = `
+"
+		
+<a>
+Random Link
+</a>
+	"
+`;

test/e2e/specs/compatibility-classic-editor.test.js

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+/**
+ * Internal dependencies
+ */
+import { newPost, insertBlock, publishPost } from '../support/utils';
+
+describe( 'Compatibility with Classic Editor', () => {
+	beforeEach( async () => {
+		await newPost();
+	} );
+
+	it( 'Should not apply autop when rendering blocks', async () => {
+		// Save should not be an option for new empty post.
+		expect( await page.$( '.editor-post-save-draft' ) ).toBe( null );
+
+		// Add title to enable valid non-empty post save.
+		await insertBlock( 'Custom HTML' );
+		await page.keyboard.type( '<a>' );
+		await page.keyboard.press( 'Enter' );
+		await page.keyboard.type( 'Random Link' );
+		await page.keyboard.press( 'Enter' );
+		await page.keyboard.type( '</a>' );
+		await publishPost();
+
+		// View the post.
+		const viewPostLinks = await page.$x( "//a[contains(text(), 'View Post')]" );
+		await viewPostLinks[ 0 ].click();
+		await page.waitForNavigation();
+
+		// Check the the dynamic block appears.
+		const content = await page.$eval( '.entry-content', ( element ) => element.innerHTML );
+		expect( content ).toMatchSnapshot();
+	} );
+} );