diff --git a/src/build-manifest.js b/src/build-manifest.js
index 559facc..a1572ca 100644
--- a/src/build-manifest.js
+++ b/src/build-manifest.js
@@ -1,18 +1,23 @@
 const fs = require("fs");
 const path = require("path");
 const iptc = require("node-iptc");
+const { exit } = require("process");
 
 
-// find all images
+// Fetch envs to target the right folder
 const slug = process.env["PACKAGE_NAME"];
 const root = process.env["ENTRY_FOLDER"];
+if (!slug || !root) exit(1);
 let workingDirectory = path.join(root, slug);
 
 // extract metadata from them
 fs.readdir(workingDirectory, (err, files) => {
-	if (err) { throw err };
+	if (err) { throw err };	// If IO error, exit with an error message
 
-	// construct a JSON file
+	// If there is already a theme.json silentely exit and let mocha running afterwards
+	if (!files.find(file => path.extname(file) == '.json')) exit(0);
+
+	// construct a JSON object
 	let theme = new Object();
 	theme.dayImageList = [];
 	theme.nightImageList = [];
@@ -63,7 +68,7 @@ fs.readdir(workingDirectory, (err, files) => {
 				break;
 		}
 	});
-
+	// make it the theme.json
 	fs.writeFileSync(path.join(workingDirectory, 'theme.json'), JSON.stringify(theme));
 });