Add tests

packages/ffmpeg/tests/test-helper.js

@@ -0,0 +1,10 @@
+const chai = require("chai");
+const constants = require("../tests/constants");
+
+global.expect = chai.expect;
+global.createFFmpeg = require("..");
+global.atob = (b64) => Buffer.from(b64, "base64").toString("binary");
+
+Object.keys(constants).forEach((key) => {
+  global[key] = constants[key];
+});