Hi Sandeep,

Defining classes of test methods with the isTest annotation
Class must be private
Use the isTest class annotation to define classes that only contain code used for testing your application
@isTest
private class Test_class {
code_block;
}
Test methods are declared with the following syntax:

static testMethod void test_name() {
code_block;
}
When you create a test method,
Use static
Use testMethod keyword
Use void return type
No any arguments
No data changes performed in a test method
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The key methods to use in your unit tests are the system.assert() methods:
System.assert(condition)
System.assertEquals(x,y)
System.assertNotEquals(x,y)
Test methods cannot be used to test Web service callouts. Web service callouts are asynchronous, while unit tests are synchronous.
Salesforce.com recommends that you write tests for the following;
Single action
Bulk action
Positive behavior
Negative behavior
Restricted user

Best Practice for writing Test Classes
·Write fully portable tests ·       
Don’t use production data in your tests · 
Test expected behavior first, then test unexpected behavior ·       
If you find a bug, write a test to expose it before you fix it ·       
Shoot for 100% coverage ·       
Don’t rely on Today() ·       
Put your tests on the controller and class, not in separate classes

http://gokubi.com/archives/testing-best-practices


Thanks,
Rajesh