Throw if there are more than one instrument enhancer included

Author: zalmoxisus

src/instrument.js

@@ -343,6 +343,10 @@ export default function instrument(monitorReducer = () => null) {
     }
 
     const liftedStore = createStore(liftReducer(reducer), undefined, enhancer);
+    if (liftedStore.liftedStore) {
+      throw new Error('DevTools instrument shouldn\'t be included more than once. ' +
+        'Check your store configuration.');
+    }
     return unliftStore(liftedStore, liftReducer);
   };
 }

test/instrument.spec.js

@@ -1,5 +1,5 @@
 import expect, { spyOn } from 'expect';
-import { createStore } from 'redux';
+import { createStore, compose } from 'redux';
 import instrument, { ActionCreators } from '../src/instrument';
 
 function counter(state = 0, action) {
@@ -328,4 +328,9 @@ describe('instrument', () => {
       instrument()(createStore)()
     ).toThrow('Expected the nextReducer to be a function.');
   });
+  it('throws if there are more than one instrument enhancer included', () => {
+    expect(() => {
+      store = createStore(counter, undefined, compose(instrument(), instrument()));
+    }).toThrow('DevTools instrument shouldn\'t be included more than once. Check your store configuration.');
+  });
 });