Promise reject instead of throwing Error

src/rollup.js

@@ -9,11 +9,11 @@ export const VERSION = '<@VERSION@>';
 
 export function rollup ( options ) {
 	if ( !options || !options.entry ) {
-		throw new Error( 'You must supply options.entry to rollup' );
+		return Promise.reject( new Error( 'You must supply options.entry to rollup' ) );
 	}
 
 	if ( options.transform || options.load || options.resolveId || options.resolveExternal ) {
-		throw new Error( 'The `transform`, `load`, `resolveId` and `resolveExternal` options are deprecated in favour of a unified plugin API. See https://github.com/rollup/rollup/wiki/Plugins for details' );
+		return Promise.reject( new Error( 'The `transform`, `load`, `resolveId` and `resolveExternal` options are deprecated in favour of a unified plugin API. See https://github.com/rollup/rollup/wiki/Plugins for details' ) );
 	}
 
 	const bundle = new Bundle( options );

test/test.js

@@ -47,13 +47,13 @@ describe( 'rollup', function () {
 		});
 
 		it( 'fails without options or options.entry', function () {
-			assert.throws( function () {
-				rollup.rollup();
-			}, /must supply options\.entry/ );
+			rollup.rollup().catch( function (err) {
+				assert( /must supply options\.entry/.test( err.toString() ) );
+			});
 
-			assert.throws( function () {
-				rollup.rollup({});
-			}, /must supply options\.entry/ );
+			rollup.rollup().catch( function (err) {
+				assert( /must supply options\.entry/.test( err.toString() ) );
+			});
 		});
 	});