From f99b2fbfb2711f71c507f917bad983d51f64c75a Mon Sep 17 00:00:00 2001
From: David Katz <15Dkatz@shcp.edu>
Date: Tue, 27 Sep 2022 14:36:21 -0700
Subject: [PATCH] Chain Validation | Tests

---
 blockchain.test.js | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/blockchain.test.js b/blockchain.test.js
index 7422d32..1bd3f01 100644
--- a/blockchain.test.js
+++ b/blockchain.test.js
@@ -2,7 +2,11 @@ const Blockchain = require('./blockchain');
 const Block = require('./block');
 
 describe('Blockchain', () => {
-  const blockchain = new Blockchain();
+  let blockchain;
+
+  beforeEach(() => {
+    blockchain = new Blockchain();
+  });
 
   it('contains a `chain` Array instance', () => {
     expect(blockchain.chain instanceof Array).toBe(true);
@@ -18,4 +22,44 @@ describe('Blockchain', () => {
 
     expect(blockchain.chain[blockchain.chain.length-1].data).toEqual(newData);
   });
+
+  describe('isValidChain()', () => {
+    describe('when the chain does not start with the genesis block', () => {
+      it('returns false', () => {
+        blockchain.chain[0] = { data: 'fake-genesis' };
+
+        expect(Blockchain.isValidChain(blockchain.chain)).toBe(false);
+      });
+    });
+
+    describe('when the chain starts with the genesis block and has multiple blocks', () => {
+      beforeEach(() => {
+        blockchain.addBlock({ data: 'Bears' });
+        blockchain.addBlock({ data: 'Beets' });
+        blockchain.addBlock({ data: 'Battlestar Galactica' });
+      });
+
+      describe('and a lastHash reference has changed', () => {
+        it('returns false', () => {
+          blockchain.chain[2].lastHash = 'broken-lastHash';
+
+          expect(Blockchain.isValidChain(blockchain.chain)).toBe(false);
+        });
+      });
+
+      describe('and the chain contains a block with an invalid field', () => {
+        it('returns false', () => {
+          blockchain.chain[2].data = 'some-bad-and-evil-data';
+
+          expect(Blockchain.isValidChain(blockchain.chain)).toBe(false);
+        });
+      });
+
+      describe('and the chain does not contain any invalid blocks', () => {
+        it('returns true', () => {
+          expect(Blockchain.isValidChain(blockchain.chain)).toBe(true);
+        });
+      });
+    });
+  });
 });