Genericize error message and create a test to ensure the correct pare…

…nt ID is returned in the error message.

src/wp-includes/rest-api/endpoints/class-wp-rest-revisions-controller.php

@@ -407,7 +407,7 @@ public function get_item( $request ) {
 			return new WP_Error(
 				'rest_revision_parent_id_mismatch',
 				/* translators: %d: A post revision id. */
-				sprintf( __( 'Parent does not have a revision with id of "%d"' ), $request['id'] ),
+				sprintf( __( 'The revision does not belong to the specified parent with id of "%d"' ), $parent->ID ),
 				array( 'status' => 404 )
 			);
 		}

tests/phpunit/tests/rest-api/rest-revisions-controller.php

@@ -276,6 +276,9 @@ public function test_get_item_invalid_parent_id() {
 		$request  = new WP_REST_Request( 'GET', '/wp/v2/posts/' . self::$post_id . '/revisions/' . $this->revision_2_1_id );
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertErrorResponse( 'rest_revision_parent_id_mismatch', $response, 404 );
+
+		$expected_message = 'The revision does not belong to the specified parent with id of "' . self::$post_id . '"';
+		$this->assertSame( $expected_message, $response->as_error()->get_error_messages()[0], 'The message must contain the correct parent ID.' );
 	}
 
 	public function test_delete_item() {

tests/phpunit/tests/rest-api/wpRestTemplateRevisionsController.php

@@ -382,6 +382,9 @@ public function test_get_item_invalid_parent_id() {
 
 		$response = rest_get_server()->dispatch( $request );
 		$this->assertErrorResponse( 'rest_revision_parent_id_mismatch', $response, 404 );
+
+		$expected_message = 'The revision does not belong to the specified parent with id of "' . self::$template_post_2->ID . '"';
+		$this->assertSame( $expected_message, $response->as_error()->get_error_messages()[0], 'The message must contain the correct parent ID.' );
 	}
 
 	/**