Add a test for loading config when the drive letter doesn't match after realpath. List 'fs' as external dependency.

rollup.config.cli.js

@@ -22,6 +22,7 @@ export default {
 		})
 	],
 	external: [
+		'fs',
 		'path',
 		'module',
 		'source-map-support'

test/cli/config-cwd-case-insensitive/_config.js

@@ -0,0 +1,13 @@
+var os = require( 'os' );
+
+function toggleCase ( s ) {
+  return ( s == s.toLowerCase() ) ? s.toUpperCase() : s.toLowerCase();
+}
+
+module.exports = {
+  skip: os.platform() !== 'win32',
+	description: "can load config with cwd that doesn't match realpath",
+	command: 'rollup -c',
+  cwd: process.cwd().replace( /^[A-Z]:\\/ig, toggleCase ),
+	execute: true
+};

test/cli/config-cwd-case-insensitive/main.js

@@ -0,0 +1 @@
+assert.equal( ANSWER, 42 );

test/cli/config-cwd-case-insensitive/rollup.config.js

@@ -0,0 +1,9 @@
+var replace = require( 'rollup-plugin-replace' );
+
+module.exports = {
+	entry: 'main.js',
+	format: 'cjs',
+	plugins: [
+		replace({ 'ANSWER': 42 })
+	]
+};

test/test.js

@@ -376,7 +376,7 @@ describe( 'rollup', function () {
 				var config = loadConfig( CLI + '/' + dir + '/_config.js' );
 
 				( config.skip ? it.skip : config.solo ? it.only : it )( dir, function ( done ) {
-					process.chdir( path.resolve( CLI, dir ) );
+					process.chdir( config.cwd || path.resolve( CLI, dir ) );
 
 					const command = 'node ' + path.resolve( __dirname, '../bin' ) + path.sep + config.command;