E2E Test Utils: Handle both plaintext and HTML errors

packages/e2e-test-utils/src/has-page-error.js

@@ -5,7 +5,7 @@
  *
  * @type {RegExp}
  */
-const REGEXP_PHP_ERROR = /<b>(Fatal error|Recoverable fatal error|Warning|Parse error|Notice|Strict Standards|Deprecated|Unknown error)<\/b>:  /;
+const REGEXP_PHP_ERROR = /(Fatal error|Recoverable fatal error|Warning|Parse error|Notice|Strict Standards|Deprecated|Unknown error)(<\/b>)?: (.*?) in (.*?) on line /;
 
 /**
  * Returns a promise resolving to a boolean reflecting whether a PHP notice is

packages/e2e-test-utils/src/test/has-page-error.js

@@ -0,0 +1,44 @@
+/**
+ * Internal dependencies
+ */
+import { hasPageError } from '../has-page-error';
+
+describe( 'hasPageError', () => {
+	let originalPage;
+
+	beforeEach( () => {
+		originalPage = global.page;
+	} );
+
+	afterEach( () => {
+		global.page = originalPage;
+	} );
+
+	it( 'returns false if there is no error', async () => {
+		global.page = {
+			content: () => 'Happy!',
+		};
+
+		expect( await hasPageError() ).toBe( false );
+	} );
+
+	it.each( [
+		[
+			'PHP, HTML',
+			'<b>Notice</b>:  Undefined property: WP_Block_Type_Registry::$x in <b>/var/www/html/wp-content/plugins/gutenberg/lib/blocks.php</b> on line <b>47</b><br />',
+		],
+		[
+			'PHP, Plaintext',
+			'Notice: Undefined property: WP_Block_Type_Registry::$x in /var/www/html/wp-content/plugins/gutenberg/lib/blocks.php on line 47',
+		],
+	] )(
+		'returns true if there is an error (%s)',
+		async ( _variant, error ) => {
+			global.page = {
+				content: () => error,
+			};
+
+			expect( await hasPageError() ).toBe( true );
+		}
+	);
+} );