add regression test to prove non-leakage

Author: timse

test/unit/errors.js

@@ -5,9 +5,11 @@ describe('prop-types', () => {
 
   it('no react', () => {
     expect(() => reactify(document.registerElement('x-errors-1'), { React: null })).to.throw(msg);
+    expect(() => reactify(document.registerElement('x-no-errors-1'))).to.not.throw(msg);
   });
 
   it('no react-dom', () => {
     expect(() => reactify(document.registerElement('x-errors-2'), { ReactDOM: null })).to.throw(msg);
+    expect(() => reactify(document.registerElement('x-no-errors-2'))).to.not.throw(msg);
   });
 });