diff --git a/src/module/module.js b/src/module/module.js
index cb189f02c..e856333d0 100644
--- a/src/module/module.js
+++ b/src/module/module.js
@@ -1,11 +1,16 @@
 import { forEachValue } from '../util'
 
+// Base data struct for store's module, package with some attribute and method
 export default class Module {
   constructor (rawModule, runtime) {
     this.runtime = runtime
+    // Store some children item
     this._children = Object.create(null)
+    // Store the origin module object which passed by programmer
     this._rawModule = rawModule
     const rawState = rawModule.state
+
+    // Store the origin module's state
     this.state = (typeof rawState === 'function' ? rawState() : rawState) || {}
   }
 
diff --git a/test/unit/module/module.spec.js b/test/unit/module/module.spec.js
index 5905c7f10..fc619a012 100644
--- a/test/unit/module/module.spec.js
+++ b/test/unit/module/module.spec.js
@@ -21,9 +21,156 @@ describe('Module', () => {
   })
 
   it('get namespacer: namespace option is true', () => {
-    const module = new Module({
+    let module = new Module({
       namespaced: true
     })
     expect(module.namespaced).toBe(true)
+
+    module = new Module({
+      namespaced: 100
+    })
+    expect(module.namespaced).toBe(true)
+  })
+
+  it('add child method', () => {
+    const module = new Module({})
+
+    module.addChild('v1', new Module({}))
+    module.addChild('v2', new Module({}))
+    expect(Object.keys(module._children)).toEqual(['v1', 'v2'])
+  })
+
+  it('remove child method', () => {
+    const module = new Module({})
+
+    module.addChild('v1', new Module({}))
+    module.addChild('v2', new Module({}))
+    expect(Object.keys(module._children)).toEqual(['v1', 'v2'])
+    module.removeChild('v2')
+    module.removeChild('abc')
+    expect(Object.keys(module._children)).toEqual(['v1'])
+  })
+
+  it('get child method', () => {
+    const module = new Module({})
+
+    const subModule1 = new Module({ state: { name: 'v1' }})
+    const subModule2 = new Module({ state: { name: 'v2' }})
+    module.addChild('v1', subModule1)
+    module.addChild('v2', subModule2)
+    expect(module.getChild('v2')).toEqual(subModule2)
+    expect(module.getChild('v1')).toEqual(subModule1)
+  })
+
+  it('update method', () => {
+    const originObject = {
+      state: {
+        name: 'vuex',
+        version: '2.x.x'
+      },
+      namespaced: true,
+      actions: {
+        a1: () => {},
+        a2: () => {}
+      },
+      mutations: {
+        m1: () => {},
+        m2: () => {}
+      },
+      getters: {
+        g1: () => {},
+        g2: () => {}
+      }
+    }
+    const newObject = {
+      actions: {
+        a3: () => {},
+        a4: () => {}
+      },
+      mutations: {
+        m3: () => {},
+        m2: () => {}
+      },
+      getters: {
+        g1: () => {}
+      },
+      namespaced: false,
+      state: {
+        name: 'vuex',
+        version: '3.x.x'
+      }
+    }
+    const module = new Module(originObject)
+
+    expect(module._rawModule).toEqual(originObject)
+
+    module.update(newObject)
+    expect(module._rawModule.actions).toEqual(newObject.actions)
+    expect(module._rawModule.mutations).toEqual(newObject.mutations)
+    expect(module._rawModule.getters).toEqual(newObject.getters)
+    expect(module._rawModule.namespaced).toEqual(newObject.namespaced)
+    expect(module._rawModule.state).toEqual(originObject.state)
+  })
+
+  it('forEachChild method', () => {
+    const module = new Module({})
+    const module1 = new Module({})
+    const module2 = new Module({})
+
+    module.addChild('v1', module1)
+    module.addChild('v2', module2)
+
+    const collections = []
+    module.forEachChild((item) => { collections.push(item) })
+    expect(collections.length).toEqual(2)
+    expect(collections).toEqual([module2, module1])
+  })
+
+  it('forEachAction method', () => {
+    const action1 = () => {}
+    const action2 = () => {}
+
+    const module = new Module({
+      actions: {
+        action1, action2
+      }
+    })
+
+    const collections = []
+    module.forEachAction((item) => { collections.push(item) })
+    expect(collections.length).toEqual(2)
+    expect(collections).toEqual([action1, action2])
+  })
+
+  it('forEachGetter method', () => {
+    const getter1 = () => {}
+    const getter2 = () => {}
+
+    const module = new Module({
+      getters: {
+        getter1, getter2
+      }
+    })
+
+    const collections = []
+    module.forEachGetter((item) => { collections.push(item) })
+    expect(collections.length).toEqual(2)
+    expect(collections).toEqual([getter1, getter2])
+  })
+
+  it('forEachMutation method', () => {
+    const mutation1 = () => {}
+    const mutation2 = () => {}
+
+    const module = new Module({
+      mutations: {
+        mutation1, mutation2
+      }
+    })
+
+    const collections = []
+    module.forEachMutation((item) => { collections.push(item) })
+    expect(collections.length).toEqual(2)
+    expect(collections).toEqual([mutation1, mutation2])
   })
 })