Merge pull request #1715 from sinonjs/sinon-es6-module-detection

Throw meaningful error stubbing ECMAScript Module

lib/sinon/spy.js

@@ -8,6 +8,7 @@ var functionToString = require("./util/core/function-to-string");
 var getPropertyDescriptor = require("./util/core/get-property-descriptor");
 var sinonMatch = require("./match");
 var deepEqual = require("./util/core/deep-equal").use(sinonMatch);
+var isEsModule = require("./util/core/is-es-module");
 var spyCall = require("./call");
 var wrapMethod = require("./util/core/wrap-method");
 var sinonFormat = require("./util/core/format");
@@ -25,12 +26,16 @@ var callId = 0;
 function spy(object, property, types) {
     var descriptor, methodDesc;
 
+    if (isEsModule(object)) {
+        throw new TypeError("ES Modules cannot be spied");
+    }
+
     if (!property && typeof object === "function") {
         return spy.create(object);
     }
 
     if (!object && !property) {
-        return spy.create(function () { });
+        return spy.create(function () {});
     }
 
     if (!types) {

lib/sinon/stub.js

@@ -6,6 +6,7 @@ var spy = require("./spy");
 var extend = require("./util/core/extend");
 var functionToString = require("./util/core/function-to-string");
 var getPropertyDescriptor = require("./util/core/get-property-descriptor");
+var isEsModule = require("./util/core/is-es-module");
 var wrapMethod = require("./util/core/wrap-method");
 var stubEntireObject = require("./stub-entire-object");
 var throwOnFalsyObject = require("./throw-on-falsy-object");
@@ -18,6 +19,10 @@ function stub(object, property) {
         throw new TypeError("stub(obj, 'meth', fn) has been removed, see documentation");
     }
 
+    if (isEsModule(object)) {
+        throw new TypeError("ES Modules cannot be stubbed");
+    }
+
     throwOnFalsyObject.apply(null, arguments);
 
     if (object && typeof property !== "undefined" && !(property in object)) {

lib/sinon/util/core/is-es-module.js

@@ -0,0 +1,16 @@
+"use strict";
+
+/**
+ * Verify if an object is a ECMAScript Module
+ *
+ * As the exports from a module is immutable we cannot alter the exports
+ * using spies or stubs. Let the consumer know this to avoid bug reports
+ * on weird error messages.
+ */
+module.exports = function (object) {
+    return (
+        object &&
+        typeof Symbol !== "undefined" &&
+        object[Symbol.toStringTag] === "Module"
+    );
+};