DDevelopment & Design

Advisory Messages to the rescue

The most crucial part of software development is testing. It should ensure us, that our code is correct, works according to given specs, etc. There are many kinds of tests: unit tests, integration, functional. In general you should try to test the smallest possible subset of your code and be able to check the state of the objects after the test.

This seems as rather easy task, but what if you have an integration end-to-end test to perform? In most cases asserting state in integration test is rather hard due to multiple systems interoperability. Let’s focus on a specific situation.

What I needed to do the other day was write some integration test for Jms based system. The processing pipeline is easy:

  • fetch object from DB
  • process it
  • publish on JMS

some other system (X-system) polls JMS:

  • if message is found
  • fetch it (message disappears from the JMS queue)
  • do sth with it
  • Looks simple but since I didn’t have any sane access to the X-system I wanted to be sure that my object was actually put into the queue. It was not acceptable to subscribe to the queue and fetch that object in my test – it would dusrupt the flow of the whole process.

    Fortunately I’ve been using ActiveMQ and since it offers a thing called Advisory Messages I’ve decided to use just them.

    What are advisory messages? They are a set of administrative messages that are generated on a specific event, like message consumption, message delivery, topic destruction, and many more. Each type of message is delivered to a separate topic – prefixed with ActiveMQ.Advisory. Since generation of such messages may be an overhead in production systems these features are turned off by default. You need to enable specific type of advisory message for a specific jms destination. You can do this with ths configuration change to activemq.xml

    <destinationPolicy>
   <policyMap>
      <policyEntries>
        <policyEntry queue="my/test/queue" advisoryForDelivery="true" advisoryForConsumed="true"/>                                                   
        <policyEntry topic=">" producerFlowControl="true" memoryLimit="1mb">
          <pendingSubscriberPolicy>
            <vmCursor />
          </pendingSubscriberPolicy>
        </policyEntry>
      </policyEntries>
    </policyMap>
</destinationPolicy>

    As you can see, I’ve specified which advisories I want enabled. The full list of available advisories can be found here.

    Since I wanted to read messages from that topic I’ve added the following configuration to my spring context – there is one destination bean for inserting messages and one bean for advisory topic.

    <bean id="testQueue" class="org.apache.activemq.command.ActiveMQQueue" autowire="constructor">
    <constructor-arg value="my/test/queue" />
</bean>

<bean id="deliveredToTestQueueAdvisory" class="org.apache.activemq.command.ActiveMQTopic" autowire="constructor">
    <constructor-arg value="ActiveMQ.Advisory.MessageDelivered.Queue.my/test/queue" />
</bean>

    Thanks to this configuration I’ve been able to check that my message was actually delivered to the queue. There’ve been no need to worry about race conditions in consuming the message from original queue – if the X-system read the message, I’d be unable to determine if it has ever been in JMS at all.

    What’s not so nice about that:

    • advisory messages can be thought of as counters rather than debugging information
    • they don’t contain any data that would allow us to match advisory message to the original message – thou you could correlate by timestamp

    All in all, it’s a good tool to have! But perhaps you have some other thoughts on this subject? How do you test JMS?

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DDevelopment & Design

CasperJS for Java developers

Why CasperJS

Being a Java developer is kinda hard these days. Java may not be dead yet, but when keeping in sync with all the hipster JavaScript frameworks could make us feel a bit outside the playground. It’s even hard to list JavaScript frameworks with latest releases on one website.

In my current project, we are using AngularJS. It’a a nice abstraction of MV* pattern in frontend layer of any web application (we use Grails underneath). Here is a nice article with an 8-point Win List of Angular way of handling AJAX calls and updating the view. So it’s not only a funny new framework but a truly helper of keeping your code clean and neat.

But there is also another area when you can put helpful JS framework in place of plan-old-java one - functional tests. Especially when you are dealing with one page app with lots of asynchronous REST/JSON communication.

Selenium and Geb

In Java/JVM project the typical is to use Selenium with some wrapper like Geb. So you start your project, setup your CI-functional testing pipeline and… after 1 month of coding your tests stop working and being maintainable. The frameworks itselves are not bad, but the typical setup is so heavy and has so many points of failure that keeping it working in a real life project is really hard.

Here is my list of common myths about Selenium: * It allows you to record test scripts via handy GUI - maybe some static request/response sites. In modern web applications with asynchronous REST/JSON communication your tests must contain a lot of “waitFor” statements and you cannot automate where these should be included. * It allows you to test your web app against many browsers - don’t try to automate IE tests! You have to manually open your app in IE to see how it actually bahaves! * It integrates well with continuous integration servers like Jenkins - you have to setup Selenium Grid on server with X installed to run tests on Chrome or Firefox and a Windows server for IE. And the headless HtmlUnit driver lacks a lot of JS support.

So I decided to try something different and introduce a bit of JavaScript tooling in our project by using CasperJS.

Introduction

CasperJS is simple but powerful navigation scripting & testing utility for PhantomJS - scritable headless WebKit (which is an rendering engine used by Safari and Chrome). In short - CasperJS allows you to navigate and make assertions about web pages as they’d been rendered in Google Chrome. It is enough for me to automate the functional tests of my application.

If you want a gentle introduction to the world of CasperJS I suggest you to read: * Official website, especially installation guide and API * Introductionary article from CasperJS creator Nicolas Perriault * Highlevel testing with CasperJS by Kevin van Zonneveld * grails-angular-scaffolding plugin by Rob Fletcher with some working CasperJS tests

Full example

I run my test suite via following script:

casperjs test --direct --log-level=debug --testhost=localhost:8080 --includes=test/casper/includes/casper-angular.coffee,test/casper/includes/pages.coffee test/casper/specs/

casper-angular.coffe

casper.test.on "fail", (failure) ->
    casper.capture(screenshot)

testhost   = casper.cli.get "testhost"
screenshot = 'test-fail.png'

casper
    .log("Using testhost: #{testhost}", "info")
    .log("Using screenshot: #{screenshot}", "info")

casper.waitUntilVisible = (selector, message, callback) ->
    @waitFor ->
        @visible selector
    , callback, (timeout) ->
        @log("Selector [#{selector}] not visible, failing")
        withParentSelector selector, (parent) ->
            casper.log("Output of parent selector [#{parent}]")
            casper.debugHTML(parent)
        @echo message, "RED_BAR"
        @capture(screenshot)
        @test.fail(f("Wait timeout occured (%dms)", timeout))

withParentSelector = (selector, callback) ->
    if selector.lastIndexOf(" ") > 0
       parent = selector[0..selector.lastIndexOf(" ")-1]
       callback(parent)

Sample pages.coffee:

x = require('casper').selectXPath

class EditDocumentPage

    assertAt: ->
        casper.test.assertSelectorExists("div.customerAccountInfo", 'at EditDocumentPage')

    templatesTreeFirstCategory: 'ul.tree li label'
    templatesTreeFirstTemplate: 'ul.tree li a'
    closePreview: '.closePreview a'
    smallPreview: '.smallPreviewContent img'
    bigPreview: 'img.previewImage'
    confirmDelete: x("//div[@class='modal-footer']/a[1]")

casper.editDocument = new EditDocumentPage()

End a test script:

testhost = casper.cli.get "testhost" or 'localhost:8080'

casper.start "http://#{testhost}/app", ->
    @test.assertHttpStatus 302
    @test.assertUrlMatch /\/fakeLogin/, 'auto login'
    @test.assert @visible('input#Create'), 'mock login button'
    @click 'input#Create'

casper.then ->
    @test.assertUrlMatch /document#\/edit/, 'new document'
    @editDocument.assertAt()
    @waitUntilVisible @editDocument.templatesTreeFirstCategory, 'template categories not visible', ->
        @click @editDocument.templatesTreeFirstCategory
        @waitUntilVisible @editDocument.templatesTreeFirstTemplate, 'template not visible', ->
            @click @editDocument.templatesTreeFirstTemplate

casper.then ->
    @waitUntilVisible @editDocument.smallPreview, 'small preview not visible', ->
        # could be dblclick / whatever
        @mouseEvent('click', @editDocument.smallPreview)

casper.then ->
    @waitUntilVisible @editDocument.bigPreview, 'big preview should be visible', ->
        @test.assertEvalEquals ->
            $('.pageCounter').text()
        , '1/1', 'page counter should be visible'
        @click @editDocument.closePreview

casper.then ->
    @click 'button.cancel'
    @waitUntilVisible '.modal-footer', 'delete confirmation not visible', ->
        @click @editDocument.confirmDelete

casper.run ->
    @test.done()

Here is a list of CasperJS features/caveats used here:

  • Using CoffeeScript is a huge win for your test code to look neat
  • When using casper test command, beware of different (than above articles) logging setup. You can pass --direct --log-level=debug from commandline for best results. Logging is essential here since Phantom often exists without any error and you do want to know what just happened.
  • Extract your helper code into separate files and include them by using --includes switch.
  • When passing server URL as a commandline switch remember that in CoffeeScript variables are not visible between multiple source files (unless getting them via window object)
  • It’s good to override standard waitUntilVisible with capting a screenshot and making a proper log statement. In my version I also look for a parent selector and debugHTML the content of it - great for debugging what is actually rendered by the browser.
  • Selenium and Geb have a nice concept of Page Objects - an abstract models of pages rendered by your application. Using CoffeeScript you can write your own classes, bind selectors to properties and use then in your code script. Assigning the objects to casper instance will end up with quite nice syntax like @editDocument.assertAt().
  • There is some issue with CSS :first and :last selectors. I cannot get them working (but maybe I’m doing something wrong?). But in CasperJS you can also use XPath selectors which are fine for matching n-th child of some element (x("//div[@class='modal-footer']/a[1]")).
    Update: :first and :last are not CSS3 selectors, but JQuery ones. Here is a list of CSS3 selectors, all of these are supported by CasperJS. So you can use nth-child(1) is this case. Thanks Andy and Nicolas for the comments!

Working with CasperJS can lead you to a few hour stall, but after getting things working you have a new, cool tool in your box!