Add docs about $this->resetInstance()

README.md

@@ -106,7 +106,7 @@ To generate coverage report, Xdebug is needed.
 
 ## How to Write Tests
 
-As an example, a test case class for Inventory_model would be as follows:
+As an example, a test case class for `Inventory_model` would be as follows:
 
 ~~~php
 <?php
@@ -115,7 +115,7 @@ class Inventory_model_test extends TestCase
 {
     public function setUp()
     {
-        $this->CI =& get_instance();
+        $this->resetInstance();
         $this->CI->load->model('Inventory_model');
         $this->obj = $this->CI->Inventory_model;
     }

docs/FunctionAndClassReference.md

@@ -12,6 +12,7 @@ version: **master** |
 - [*function* `set_is_cli($return)`](#function-set_is_clireturn)
 - [*function* `load_class_instance($classname, $instance)`](#function-load_class_instanceclassname-instance)
 - [*class* TestCase](#class-testcase)
+	- [`TestCase::resetInstance()`](#testcaseresetinstance)
 	- [`TestCase::request($method, $argv, $params = [], $callable = null)`](#testcaserequestmethod-argv-params---callable--null)
 		- [`request->setCallable()`](#request-setcallable)
 		- [`request->setCallablePreConstructor()`](#request-setcallablepreconstructor)
@@ -46,6 +47,8 @@ $controller = new Welcome();
 $this->CI =& get_instance();
 ~~~
 
+Normally, you don't have to use this function. Use [`TestCase::resetInstance()`](#testcaseresetinstance) method instead.
+
 ### *function* `set_is_cli($return)`
 
 | param   | type | description         |
@@ -78,6 +81,36 @@ load_class_instance('email', $email);
 
 ### *class* TestCase
 
+#### `TestCase::resetInstance()`
+
+Reset CodeIgniter instance and assign new CodeIgniter instance as `$this->CI`.
+
+~~~php
+public function setUp()
+{
+	$this->resetInstance();
+	$this->CI->load->model('Category_model');
+	$this->obj = $this->CI->Category_model;
+}
+~~~
+
+**Upgrade Note for v0.6.0**
+
+Before v0.6.0, we write `setUp()` method like this:
+
+~~~php
+public function setUp()
+{
+	$this->CI =& get_instance();
+	$this->CI->load->model('Category_model');
+	$this->obj = $this->CI->Category_model;
+}
+~~~
+
+When you use the way, you use the same CodeIgniter instance and the same `Category_model` instance in every test method.
+
+In contrast, if you use `$this->resetInstance()`, it resets CodeIgniter instance and `Category_model`. So you use new CodeIgniter instance and new `Category_model` instance in every test method.
+
 #### `TestCase::request($method, $argv, $params = [], $callable = null)`
 
 | param     | type         | description                                    |

docs/HowToWriteTests.md

@@ -203,7 +203,7 @@ If you don't know well about PHPUnit Mock Objects, see [Test Doubles](https://ph
 ~~~php
 	public function setUp()
 	{
-		$this->CI =& get_instance();
+		$this->resetInstance();
 		$this->CI->load->model('Category_model');
 		$this->obj = $this->CI->Category_model;
 	}
@@ -254,14 +254,10 @@ If you don't know well about PHPUnit Mock Objects, see [Test Doubles](https://ph
 		foreach ($list as $category) {
 			$this->assertEquals($expected[$category->id], $category->name);
 		}
-
-		// Reset CI object for next test case, unless property db won't work
-		reset_instance();
-		new CI_Controller();
 	}
 ~~~
 
-**Note:** Once you have replaced CodeIgniter object's property with your mock, the mock remains until you call `reset_instance()` and instantiate a controller.
+[$this->resetInstance()](FunctionAndClassReference.md#testcaseresetinstance) method in *CI PHPUnit Test* is a helper method to reset CodeIgniter instance and assign new CodeIgniter instance as `$this->CI`.
 
 See [working sample](https://github.com/kenjis/ci-app-for-ci-phpunit-test/blob/master/application/tests/models/Category_model_mocking_db_test.php).