Is it important to include @isTest on Testing Method in Salesforce? Explain?

Hii Avnish,

Yes, it is important to denote a test class with a separate syntax so that the compiler can understand that its a class where we are going to perform a test. But, instead of using an annotation @isTest, we can also use 'testmethod'  in a method name.

Adding some points:

This class is defined using the @isTest annotation. Classes defined as such can only contain test methods. One advantage to creating a separate class for testing as opposed to adding test methods to an existing class is that classes defined with isTest don't count against your organization limit of 3 MB for all Apex code.
The advantage to using separate test classes is that they do not count against the limit of the total amount of apex in your org (although this is a soft limit and thus not a overly compelling reason).

@isTest
public class TestUtil {

public static void createTestAccounts() {
// Create some test accounts
}

public static void createTestContacts() {
// Create some test contacts
}

}

Thanks