add test for es6 format warning

test/test.js

@@ -17,7 +17,7 @@ var CLI = path.resolve( __dirname, 'cli' );
 var PROFILES = [
 	{ format: 'amd' },
 	{ format: 'cjs' },
-	{ format: 'es6' },
+	{ format: 'es' },
 	{ format: 'iife' },
 	{ format: 'umd' }
 ];
@@ -125,6 +125,26 @@ describe( 'rollup', function () {
 				}, /You must supply options\.moduleName for IIFE bundles/ );
 			});
 		});
+
+		it( 'warns on es6 format', function () {
+			var warned;
+
+			return rollup.rollup({
+				entry: 'x',
+				plugins: [{
+					resolveId: function () { return 'test'; },
+					load: function () {
+						return '// empty';
+					}
+				}],
+				onwarn: function ( msg ) {
+					if ( /The es6 format is deprecated/.test( msg ) ) warned = true;
+				}
+			}).then( function ( bundle ) {
+				bundle.generate({ format: 'es6' });
+				assert.ok( warned );
+			});
+		});
 	});
 
 	describe( 'function', function () {