Added test for mixin method & Updated README.md

Author: vramana

README.md

@@ -94,4 +94,25 @@ Test(<TestComponent/>)
 
 ~~~
 
+##mixin
+
+Use `.mixin` if you want to add new middleware as methods to `Test`. This gives a more natural way of using middleware:
+
+~~~js
+// In this example, CustomFind middleware was added to Test by mixin
+// and used if as it was a method on Test itself.
+
+Test(<TestComponent />)
+.mixin({
+  customFind: CustomFind
+})
+.customFind('cells', 'table td')
+.element('cells', cells => {
+  expect(cells.length).to.be.equal(10)
+})
+
+~~~
+
+
+
 You can see more examples in the tests directory.

tests/mixin.jsx

@@ -0,0 +1,22 @@
+import React from 'react'
+
+import Test from '../src/legit-tests'
+import { Find } from '../src/middleware'
+import { expect } from 'chai'
+
+import { TestComponent } from './components'
+
+describe('Mixin method', () => {
+
+  it('should add Find as method to Test', () => {
+    Test(<TestComponent/>)
+    .mixin({
+      customFind: Find
+    })
+    .customFind('div')
+    .element('div', div => {
+      expect(div.length).to.equal(2)
+    })
+  })
+
+})