diff --git a/js/package.json b/js/package.json
index a5fab74d5..50f512823 100644
--- a/js/package.json
+++ b/js/package.json
@@ -67,6 +67,7 @@
     "babel-register": "6.18.0",
     "babel-runtime": "6.18.0",
     "chai": "3.5.0",
+    "chai-as-promised": "6.0.0",
     "chai-enzyme": "0.6.1",
     "copy-webpack-plugin": "4.0.1",
     "core-js": "2.4.1",
diff --git a/js/src/ui/TxList/store.js b/js/src/ui/TxList/store.js
index 3faac193e..09cdd2226 100644
--- a/js/src/ui/TxList/store.js
+++ b/js/src/ui/TxList/store.js
@@ -45,6 +45,8 @@ export default class Store {
 
           if (bnB.eq(0)) {
             return bnB.eq(bnA) ? 0 : 1;
+          } else if (bnA.eq(0)) {
+            return -1;
           }
 
           return bnB.comparedTo(bnA);
diff --git a/js/src/ui/TxList/store.spec.js b/js/src/ui/TxList/store.spec.js
new file mode 100644
index 000000000..9fb3a709e
--- /dev/null
+++ b/js/src/ui/TxList/store.spec.js
@@ -0,0 +1,90 @@
+// Copyright 2015, 2016 Ethcore (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+import BigNumber from 'bignumber.js';
+import sinon from 'sinon';
+
+import Store from './store';
+
+const SUBID = 123;
+const BLOCKS = {
+  1: { blockhash: '0x1' },
+  2: { blockhash: '0x2' }
+};
+const TRANSACTIONS = {
+  '0x123': { blockNumber: new BigNumber(1) },
+  '0x234': { blockNumber: new BigNumber(0) },
+  '0x345': { blockNumber: new BigNumber(2) },
+  '0x456': { blockNumber: new BigNumber(0) }
+};
+
+describe.only('ui/TxList/store', () => {
+  let api;
+  let store;
+
+  beforeEach(() => {
+    api = {
+      subscribe: sinon.stub().resolves(SUBID),
+      eth: {
+        getBlockByNumber: (blockNumber) => {
+          return Promise.resolve(BLOCKS[blockNumber]);
+        }
+      }
+    };
+    store = new Store(api);
+  });
+
+  describe('create', () => {
+    it('has empty storage', () => {
+      expect(store.blocks).to.deep.equal({});
+      expect(store.sortedHashes.peek()).to.deep.equal([]);
+      expect(store.transactions).to.deep.equal({});
+    });
+
+    it('subscribes to eth_blockNumber', () => {
+      expect(api.subscribe).to.have.been.calledWith('eth_blockNumber');
+      expect(store._subscriptionId).to.equal(SUBID);
+    });
+  });
+
+  describe('addBlocks', () => {
+    beforeEach(() => {
+      store.addBlocks(BLOCKS);
+    });
+
+    it('adds the blocks to the list', () => {
+      expect(store.blocks).to.deep.equal(BLOCKS);
+    });
+  });
+
+  describe('addTransactions', () => {
+    beforeEach(() => {
+      store.addTransactions(TRANSACTIONS);
+    });
+
+    it('adds all transactions to the list', () => {
+      expect(store.transactions).to.deep.equal(TRANSACTIONS);
+    });
+
+    it('sorts transactions based on blockNumber', () => {
+      expect(store.sortedHashes.peek()).to.deep.equal(['0x234', '0x456', '0x345', '0x123']);
+    });
+
+    it('adds pending transactions to the pending queue', () => {
+      expect(store._pendingHashes).to.deep.equal(['0x234', '0x456']);
+    });
+  });
+});
diff --git a/js/test/mocha.config.js b/js/test/mocha.config.js
index adc43530e..36c91c76e 100644
--- a/js/test/mocha.config.js
+++ b/js/test/mocha.config.js
@@ -22,11 +22,13 @@ es6Promise.polyfill();
 import 'mock-local-storage';
 
 import chai from 'chai';
+import chaiAsPromised from 'chai-as-promised';
 import chaiEnzyme from 'chai-enzyme';
 import sinonChai from 'sinon-chai';
 import { WebSocket } from 'mock-socket';
 import jsdom from 'jsdom';
 
+chai.use(chaiAsPromised);
 chai.use(chaiEnzyme());
 chai.use(sinonChai);