oroce · September 4, 2018 11:29 · Sep 4, 2018
diff --git a/package.json b/package.json
@@ -0,0 +1,3 @@
+{
+  "scripts": "mocha -r should '*.spec.js'"
+}
diff --git a/reducer.js b/reducer.js
@@ -0,0 +1,18 @@
+export default (action, state = { sum: 0 }) => {
+  switch (action.type) {
+    case 'add': {
+      return {
+        ...state,
+        sum: state.sum + action.payload.num
+      };
+    };
+    case 'subtract': {
+      return {
+        ...state,
+        sum: state.sum - action.payload.num
+      };
+    };
+    default: {
+      return state;
+    }
+};
diff --git a/reducer.spec.js b/reducer.spec.js
@@ -0,0 +1,38 @@
+import reducer from './reducer';
+describe('reducer', () => {
+  it('should add the number to the sum', () => {
+    reducer({
+      type: 'add',
+      payload: { num: 2 }
+    }, { sum: 4 }).should.eql({
+      sum: 6
+    });
+  });
+
+  it('should not add fail with no state', () => {
+    reducer({
+      type: 'add',
+      payload: { num: 2 }
+    }).should.eql({
+      sum: 2
+    });
+  });
+
+  it('should subtract the number', () => {
+    reducer({
+      type: 'subtract',
+      payload: { num: 2 }
+    }, { sum: 4 }).should.eql({
+      sum: 2
+    });
+  });
+
+  it('should not subtract fail with no state', () => {
+    reducer({
+      type: 'subtract',
+      payload: { num: 2 }
+    }).should.eql({
+      sum: -2
+    });
+  });
+});
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