Add test : handle external is a function in config.

test/cli/config-external-function/_config.js

@@ -0,0 +1,4 @@
+module.exports = {
+	description: 'external option gets passed from config',
+	command: 'rollup -c -e assert,external-module'
+};

test/cli/config-external-function/_expected.js

@@ -0,0 +1,8 @@
+'use strict';
+
+var ___config_js = require('./_config.js');
+var assert = require('assert');
+var externalModule = require('external-module');
+
+assert.ok( ___config_js.execute );
+externalModule.method();

test/cli/config-external-function/main.js

@@ -0,0 +1,6 @@
+import { execute } from './_config.js';
+import { ok } from 'assert';
+import { method } from 'external-module';
+
+ok( execute );
+method();

test/cli/config-external-function/rollup.config.js

@@ -0,0 +1,25 @@
+import assert from 'assert';
+import { resolve, sep } from 'path';
+
+var config = resolve( './_config.js' ).split(sep).join('/');
+
+export default {
+	entry: 'main.js',
+	format: 'cjs',
+
+	external: function (id) {
+		if (id === config) {
+			return true;
+		}
+
+		return false;
+	},
+
+	plugins: [
+		{
+			load: function ( id ) {
+				assert.notEqual( id, config );
+			}
+		}
+	]
+};