add error on using duplicate reducer name

Author: IpShot

src/flexReducer.js

@@ -60,6 +60,8 @@ export function useFlexReducer(reducerName, reducer, initialState, options = { c
   if (!key.current) {
     key.current = genKey();
     reducerActiveComponent.set(reducerName, key.current);
+  } else if (reducerActiveComponent.get(reducerName) !== key.current) {
+    throw new Error(`Looks like you're trying to use more than one component with the same "${reducerName}" reducer.`);
   }
 
   const [state, render] = useState(options.cache && cache[reducerName] || initialState);

test/flex-reducer.test.js

@@ -410,7 +410,7 @@ describe('Flex Reducer', () => {
       expect(state.value).toBe('Hello Parent!')
       expect(cState.value).toBe('Bye Child!')
     })
-    it('should not throw "reducer already in use" error if one component unmounted and another with the same reducer name is mounted and both happened through the same render', () => {
+    it('should not throw duplicating error if one component unmounted and another with the same reducer name is mounted and both happened through the same render', () => {
       const Child2 = () => {
         useFlexReducer('child', cReducer, cInitialState)
         return <div />
@@ -433,6 +433,25 @@ describe('Flex Reducer', () => {
       )
       expect(result.error).not.toBe(undefined)
     })
+    it('should throw an error if reducer name is duplicating on second render', () => {
+      const Child2 = () => {
+        useFlexReducer('child', cReducer, cInitialState)
+        return <div />
+      }
+      Parent = () => {
+        useFlexReducer('parent', pReducer, pInitialState)
+        return (
+          <div>
+            <Child2 />
+            <Child />
+          </div>
+        )
+      }
+      const { rerender } = rtl.render(<Parent />)
+      expect(() => {
+        rerender(<Parent />)
+      }).toThrow('Looks like you\'re trying to use more than one component with the same "child" reducer.')
+    })
     it('should throw an error if reducer is missing', () => {
       const { result } = renderHook(
         () => useFlexReducer('parent')