static testmethod void TestMethod() {


    //Created A dummy Account and Opportunity records I.e  Acc & Opt

    //getting standard pricebook id
    Id pricebookId = Test.getStandardPricebookId();

    //Created a product
    Product2 prod = new Product2(
         Name = 'Product X',
         ProductCode = 'Pro-X',
         isActive = true,
         IsAvailable__c = True // setting field value as true
    );
    insert prod;


    //Created pricebook entry
    PricebookEntry pbEntry = new PricebookEntry(
         Pricebook2Id = pricebookId,
         Product2Id = prod.Id,
         UnitPrice = 100.00,
         IsActive = true
    );
    insert pbEntry;

    //created opportunity line item.
    OpportunityLineItem oli = new OpportunityLineItem(
         OpportunityId = opt.Id,
         units__c = 25,
         Type__c = 'No. Users',
         PricebookEntryId = pbEntry.Id,
         TotalPrice = 200,
         Quantity = 1
    );

    insert oli;

    system.debug('oli.IsAvailable__c ='+ oli.IsAvailable__c ); // This is returing me value as false

    Test.startTest();

    //calling my required methods here

    Test.stopTest();
}