add async error test

test/async.js

@@ -0,0 +1,69 @@
+var chai = require('chai');
+var assert = chai.assert;
+var web3 = require('../index');
+var FakeHttpProvider = require('./helpers/FakeHttpProvider');
+
+// use sendTransaction as dummy
+var method = 'sendTransaction';
+
+var tests = [{
+    result: '0xb',
+    formattedResult: '0xb',
+    call: 'eth_'+ method
+}];
+
+describe('async', function () {
+    tests.forEach(function (test, index) {
+        it('test: ' + index, function (done) {
+
+            // given
+            var provider = new FakeHttpProvider();
+            web3.setProvider(provider);
+            provider.injectResult(test.result);
+            provider.injectValidation(function (payload) {
+                assert.equal(payload.jsonrpc, '2.0');
+                assert.equal(payload.method, test.call);
+                assert.deepEqual(payload.params, [{}]);
+            });
+
+            // when 
+            web3.eth[method]({}, function(error, result){
+
+                // then
+                assert.isNull(error);
+                assert.strictEqual(test.formattedResult, result);
+
+                done();
+            });
+
+        });
+
+        it('error test: ' + index, function (done) {
+
+            // given
+            var provider = new FakeHttpProvider();
+            web3.setProvider(provider);
+            provider.injectError({
+                    message: test.result,
+                    code: -32603
+            });
+            provider.injectValidation(function (payload) {
+                assert.equal(payload.jsonrpc, '2.0');
+                assert.equal(payload.method, test.call);
+                assert.deepEqual(payload.params, [{}]);
+            });
+
+            // when 
+            web3.eth[method]({}, function(error, result){
+
+                // then
+                assert.isUndefined(result);
+                assert.strictEqual(test.formattedResult, error.message);
+
+                done();
+            });
+
+        });
+    });
+});
+