I recently figured out how to use WebTest for functional testing of Grails controller actions that render JSON. That said, I’m not convinced it’s the best way – I’m fairly sure the gFunc plugin would do it nicely, though I ran into problems with it clean compiling the whole app on every run.

Custom steps

It’s been possible to add custom steps to Webtests for some time. Assuming you have v0.6 of the plugin (or you use Grails 1.1), then this writeup provides some useful background and also a ‘Hello, World’ type example.

In an ideal world

On the surface it seems that we could therefore have a jsonVerify step which is quite simply:

class JsonVerifyStep extends Step {

    String expected

    void doExecute() {
        def jsonServed = context.currentResponse.inputStream as JSON
        def jsonExpected = expected as JSON
        assert jsonExpected, jsonServed
    }

}

Annoyingly, it’s not this easy.

Grails, Webtest and (sigh) Classpath’s

Webtest is spawned by a forked Ant process (see ${pluginDir}/webtest-n.n/scripts/call-webtest.xml) which means you get a  limited classpath due to JAR version conflicts.

So it’s not possible to add the Grails classpath (or even just $GRAILS_HOME/dist/grails-web-n.n.jar) which contains all the handy JSON library code that we’re so accustomed to when rendering JSON responses.

Solution (has some camembert)

My “solution” was to add two jars (json-lib & ezmorph) to your Grails lib and also tweak the call-webtest.xml file with the following change:

<fileset dir="${grailsHome}/lib" includes="commons-cli*.jar,commons-beanutils*.jar"/>

With the resulting custom step you can test your JSON response

import com.canoo.webtest.steps.Step
import net.sf.json.JSON
import net.sf.json.groovy.GJson
import org.apache.commons.io.IOUtils
import org.apache.log4j.Logger
import net.sf.json.test.JSONAssert

class JsonVerifyStep extends Step {
    private static Logger log = Logger.getLogger(JsonVerifyStep)

    String expected

    void doExecute() {
        GJson.enhanceClasses() // neccessary for the net.sf.JSON stuff in Groovy
        def jsonServed = IOUtils.toString(context.currentResponse.inputStream) as JSON // wants a string
        def jsonExpected = expected as JSON
        JSONAssert.assertEquals jsonExpected, jsonServed
    }
}

And you would implement your webtest as follows:

    def testSomeJSONResponse() {
        webtest('Example JSON webtest') {
            invoke('/controller/actionJSON')
            jsonVerify(expected: '{"totalRecords":2,"results":[{"id":16,"year":2009,"name":"ZZ Top"},{"id":2,"year":2009,"name":"Aerosmith"}')
        }

    }