BlockChainTest.cls

@isTest
public class BlockChainTest{

    //Testing Blockchain 
    @isTest
    public static void testBlockChain(){
        /**Data Setup**/
        
        //Creating Instance of Blockchain
        BlockChain bChain = new BlockChain();
    
        //addBlock method take data as the string
        //Changing data to the string with the JSON format
        
        //Adding the first block to the chain
        bChain.addBlock( json.serialize( new BCTestDataWrapper('Iron Man', '2334343434') ) );
        
        //Adding the second block to the chain
        bChain.addBlock( json.serialize( new BCTestDataWrapper('Thor', '34343434') ) );
        
        
        /**Positive Testing**/
        
        //isChainValid will return true, as no data has been modified from block
        system.assertEquals(true, bChain.isChainValid() );
        
        //Print Blockchain
        system.debug('-Blockchain Data Before Modifying--'+Json.serialize( bChain.chain) );
        
        
        /**Negative Testing**/
        
        //Now updating the 0 index's block
        BCTestDataWrapper tData = (BCTestDataWrapper)JSON.deserialize(bChain.chain[0].data, BCTestDataWrapper.class);
        tData.name = 'Thanos';
        bChain.chain[0].data = json.serialize(tData);
        
        //isChainValid will return false, as the data has been modified from block
        system.assertEquals(false, bChain.isChainValid() );
        
        //Print Blockchain
        system.debug('-Blockchain Data After Modifying--'+Json.serialize( bChain.chain) );
    }
}