Angel \”Java\” Lopez on Blog

May 23, 2016

Building A Blockchain (10)

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This week, I added more logic to my personal blockchain project in JavaScript:

https://github.com/ajlopez/SimpleBlockchain

I started to implement the blockchain logic using TDD (Test-Driven Development) workflow. A first test creating the blockchain object using a genesis block:

var blockchains = require('../lib/blockchains');
var blocks = require('../lib/blocks');

exports['create blockchain'] = function (test) {
    var genesis = blocks.block();
    var bc = blockchains.blockchain(genesis);
    
    test.ok(bc);
    test.equal(typeof bc, 'object');
    test.equal(bc.bestBlock(), genesis);
};

Then, I wrote a test exercising to add a new block:

exports['add block'] = function (test) {
    var genesis = blocks.block();
    var block = blocks.block(genesis);
    var bc = blockchains.blockchain(genesis);
    
    bc.add(block);
    
    test.equal(bc.bestBlock(), block);
};

The rejection of a block of the same height than the best block in blockchain:

exports['add block same height'] = function (test) {
    var genesis = blocks.block();
    var block = blocks.block(genesis);
    var block2 = blocks.block(genesis);
    
    var bc = blockchains.blockchain(genesis);
    
    bc.add(block);
    bc.add(block2);
    
    test.equal(bc.bestBlock(), block);
};

The adding of a block that is a child of the best block, and the rejection of a block that is not the descendant of the best block:

exports['add block with next height'] = function (test) {
    var genesis = blocks.block();
    var block = blocks.block(genesis);
    var block2 = blocks.block(block);
    
    var bc = blockchains.blockchain(genesis);
    
    bc.add(block);
    bc.add(block2);
    
    test.equal(bc.bestBlock(), block2);
};

exports['add block next height but another parent block'] = function (test) {
    var genesis = blocks.block();
    var block = blocks.block(genesis);
    var block2 = blocks.block(genesis);
    var block3 = blocks.block(block2);
    
    var bc = blockchains.blockchain(genesis);
    
    bc.add(block);
    bc.add(block3);
    
    test.equal(bc.bestBlock(), block);
};

These tests were written one by one, and each test was followed by the simplest implementation that pass the test. This is the spirit of TDD: baby steps, simple implementation, explicit description of expected behavior.

Next post: implementing account states, immutable states, and node communication.

Stay tuned!

Angel “Java” Lopez

http://www.ajlopez.com

http://twitter.com/ajlopez

2 Comments »

  1. […] Previous Post Next Post […]

    Pingback by Building A Blockchain (9) | Angel "Java" Lopez on Blog — May 23, 2016 @ 8:47 am

  2. […] Previous Post […]

    Pingback by Building A Blockchain (11) | Angel "Java" Lopez on Blog — May 30, 2016 @ 10:18 am


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