[docs] Add testing section

docs/src/docs/08-testing.md

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+---
+title: "Testing"
+section: "Guide"
+---
+
+# Testing
+
+The most valuable and easy to write tests for NuclearJS are unit tests.  **The unit in Nuclear is the action.** The key assertion we want to make 
+is that a particular action or set of actions properly transforms the Reactor from **State A** to **State B**.
+
+This is done by setting up the reactor with the proper state, using actions, executing the action under test and asserting proper state via **Getters**.
+
+## Example
+
+In our testing example we will test our Project module while contains two stores, the `currentProjectIdStore` and the `projectStore` as well as
+actions and getters.
+
+#### `index.js`
+
+```javascript
+import reactor from '../reactor'
+import projectStore from './stores/projectStore'
+import currentProjectIdStore from './stores/currentProjectIdStore'
+import actions from './actions'
+import getters from './getters'
+
+reactor.registerStores({
+  currentProjectId: currentProjectIdStore,
+  projects: projectStore,
+})
+
+export default { getters, actions }
+```
+
+#### `stores/currentProjectIdStore.js`
+
+```javascript
+import { Store } from 'nuclear-js'
+import { CHANGE_CURRENT_PROJECT_ID } from '../actionTypes'
+
+export default Store({
+  getInitialState() {
+    return null
+  },
+
+  initialize() {
+    this.on(CHANGE_CURRENT_PROJECT_ID, (currentId, newId) => newId)
+  },
+})
+```
+
+#### `stores/projectStore.js`
+
+```javascript
+import { Store, toImmutable } from 'nuclear-js'
+import { LOAD_PROJECTS } from '../actionTypes'
+
+export default Store({
+  getInitialState() {
+    // will maintain a map of project id => project object
+    return toImmutable({})
+  },
+
+  initialize() {
+    this.on(LOAD_PROJECTS, loadProjects)
+  },
+})
+
+/**
+ * @param {Immutable.Map} state
+ * @param {Object} payload
+ * @param {Object[]} payload.data
+ * @return {Immutable.Map} state
+ */
+function loadProjects(state, payload) {
+  return state.withMutations(state => {
+    payload.forEach(function(project) {
+      state.set(project.id, project)
+    })
+  })
+}
+```
+
+#### `actions.js`
+
+```javascript
+import Api from '../utils/api'
+import reactor from '../reactor'
+import { LOAD_PROJECTS } from './actionTypes'
+
+export default {
+  fetchProjects() {
+    return Api.fetchProjects.then(projects => {
+      reactor.dispatch(LOAD_PROJECTS, {
+        data: projects,
+      })
+    })
+  },
+
+  /**
+   * @param {String} id
+   */
+  setCurrentProjectId(id) {
+    reactor.dispatch(CHANGE_CURRENT_PROJECT_ID, id)
+  },
+}
+```
+
+#### `getters.js`
+
+```
+cosnt projectsMap = ['projects']
+
+const currentProjectId = ['currentProjectId']
+
+const currentProject = [
+  currentProjectId,
+  projectsMap,
+  (id, projects) => projects.get(id)
+]
+
+export default { projectsMap, currentProject, currentProjectId }
+```
+
+### Tests
+
+Given our module we want to test the following:
+
+- Using `actions.setCurrentProjectId()` sets the correct id using the `currentProjectId` getter
+
+- When `Api.fetchProducts` is stubbed with mock data, calling `actions.fetchProjects` properly poulates
+  the projects store by using the `projectsMap` getter
+
+- When projects have been loaded and currentProjectId set, `currentProject` getter works
+
+**Testing Tools**
+
+We will use the following tools: mocha, sinon, expect.js.  The same testing ideas can be implemented with a variety of tools.
+
+#### `tests.js`
+
+```javascript
+import reactor from '../reactor'
+import Api from '../utils/api'
+import expect from 'expect'
+
+// module under test
+import Project from './index'
+
+let mockProjects = [
+  { id: '123-abc', name: 'project 1' },
+  { id: '456-cdf', name: 'project 2' },
+]
+
+describe('modules/Project', () => {
+  afterEach(() => {
+    flux.reset()
+  })
+
+  describe('actions', () => {
+    describe('#setCurrentProjectId', () => {
+      it("should set the current project id", () => {
+        Project.actions.setCurrentProjectId('123-abc')
+
+        expect(flux.evaluate(Project.getters.currentProjectId)).to.be('123-abc')
+      })
+    })
+
+    describe('#fetchProjects', () => {
+      beforeEach(() => {
+        let fetchProjectsPromise = new Promise((resolve, reject) => {
+          resolve(mockProjects)
+        })
+
+        sinon.stub(Api, 'fetchProjects').returns(fetchProjectsPromise)
+      })
+
+      afterEach(() => {
+        Api.fetchProjects.restore()
+      })
+
+      it('should load projects into the project store', (done) => {
+        Project.actions.fetchProjects().then(() => {
+          projectsMap = flux.evaluateToJS(Project.getters.projectMap)
+          expect(projectsMap).to.eql({
+            '123-abc': { id: '123-abc', name: 'project 1' },
+            '456-cdf': { id: '456-cdf', name: 'project 2' },
+          })
+          done()
+        })
+      })
+    })
+  })
+
+  describe('getters', () => {
+    describe('#currentProject', () => {
+      beforeEach((done) => {
+        let fetchProjectsPromise = new Promise((resolve, reject) => {
+          resolve(mockProjects)
+        })
+        sinon.stub(Api, 'fetchProjects').returns(fetchProjectsPromise)
+
+        // wait for the projects to be fetched / loaded into store before test
+        Project.actions.fetchProjects().then(() => {
+          done()
+        })
+      })
+
+      afterEach(() => {
+        Api.fetchProjects.restore()
+      })
+
+      it('should evaluate to the current project when the currentProjectId is set', () => {
+        expect(flux.evaluate(Project.getters.currentProject)).to.be(undefined)
+
+        Project.actions.setCurrentProjectId('123-abc')
+
+        expect(flux.evaluateToJS(Project.getters.currentProject)).to.eql({
+          id: '123-abc',
+          name: 'project 1',
+        })
+      })
+    })
+  })
+})
+```
+
+## Recap
+
+When testing NuclearJS code it makes sense to test around actions asserting proper state updates via getters.  While these tests may seem simple, they are
+testing that our stores, actions and getters are all working in a cohesive manner.  As your codebase scales out these tests be the foundation of unit tests
+for all data flow and state logic.
+
+Another thing to note is that we did not stub or mock any part of the NuclearJS system.  While testing in isolation is good for a variety of reasons,
+isolating too much will cause your tests to be unrealistic and more prone to breakage after refactoring.  By testing the entire module as a unit
+we are able to keep the test high level with limited stubs.