Improve code quality and write tests

node_modules/@babel/helper-module-imports/lib/is-module.js

@@ -0,0 +1,18 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = isModule;
+
+function isModule(path) {
+  const {
+    sourceType
+  } = path.node;
+
+  if (sourceType !== "module" && sourceType !== "script") {
+    throw path.buildCodeFrameError(`Unknown sourceType "${sourceType}", cannot transform.`);
+  }
+
+  return path.node.sourceType === "module";
+}