add: unit and integration testing

app/node_modules/path-exists/index.js

@@ -0,0 +1,23 @@
+'use strict';
+const fs = require('fs');
+const {promisify} = require('util');
+
+const pAccess = promisify(fs.access);
+
+module.exports = async path => {
+	try {
+		await pAccess(path);
+		return true;
+	} catch (_) {
+		return false;
+	}
+};
+
+module.exports.sync = path => {
+	try {
+		fs.accessSync(path);
+		return true;
+	} catch (_) {
+		return false;
+	}
+};