Don't insert the same node into the AST multiple times (fixes babel/babili#556) (#6054)

packages/babel-plugin-transform-es2015-modules-commonjs/test/copied-nodes.js

@@ -0,0 +1,19 @@
+const assert = require("assert");
+const babel = require("babel-core");
+
+test("Doesn't use the same object for two different nodes in the AST", function() {
+  const code = 'import Foo from "bar"; Foo; Foo;';
+
+  const ast = babel.transform(code, {
+    plugins: [[require("../"), { loose: true }]],
+  }).ast;
+
+  assert.equal(ast.program.body[3].expression.type, "MemberExpression");
+  assert.equal(ast.program.body[4].expression.type, "MemberExpression");
+
+  assert.notEqual(
+    ast.program.body[3].expression,
+    ast.program.body[4].expression,
+    "Expected different nodes in the AST to not be the same object",
+  );
+});