Using Schedulable interface Testclass

@isTest 
public class ContractAmendmentLinkageTestClass{
@isTest static void Amendment(){
ContractAmendmentLinkage Contractobj = new ContractAmendmentLinkage ();
String sch = '20 30 8 10 2 ?';
String jobID = system.schedule('ContractAmendmentLinkage JOB', sch, Contractobj);

Datetime sysTime = System.now().addSeconds( 300 );     
String chronExpression = '' + sysTime.second() + ' ' + sysTime.minute() + ' ' + sysTime.hour() + ' ' + sysTime.day() + ' ' + sysTime.month() + ' ? ' + sysTime.year();
System.Schedule('SelfSchedule ' + sysTime, chronExpression, new ContractAmendmentLinkage() );
  }
}

sch: Is the corn expression ,the corn expression is nothing but the next scheduled time.
ContractAmendmentLinkage JOB: is the name of the job.
Contractobj:: is the object of the scheduled class which we need to run.
corn expression for to run schedule(ContractAmendmentLinkage) every 5min. below

// This is Self-Schedule To Execution purpose.

(Datetime sysTime = System.now().addSeconds( 300 );   
String chronExpression = '' + sysTime.second() + ' ' + sysTime.minute() + ' ' + sysTime.hour() + ' ' + sysTime.day() + ' ' + sysTime.month() + ' ? ' + sysTime.year();
System. Schedule( 'SelfSchedule ' + sysTime, chronExpression, new ContractAmendmentLinkage() );)