How can I cover exception part in a class using test class in Salesforce?

Hi,

In your testmethod, insert records in such a way that it will cause the exception to occur. This will cover the exception lines as well.

try this in your test class.

try
{
//perform actions like insert,update,delete...etc that causes your exception to occur
system.assert(false);
}
Catch(exception e)
{

}

Thanks.