BrowserInstance.groovy

package spock

import org.openqa.selenium.remote.RemoteWebDriver

@Singleton
class BrowserInstance {
    def RemoteWebDriver driver
}

BrowserStackListener.groovy

class BrowserStackListener extends AbstractRunListener {

    void error(ErrorInfo error) {

        if (!BrowserInstance.instance.driver) {
            return
        }

        def username = getenv("BROWSERSTACK_USER")
        def accessKey = getenv("BROWSERSTACK_ACCESSKEY")
        def sessionId = BrowserInstance.instance.driver.getSessionId().toString()

        def reportUrl = "https://${username}:${accessKey}@api.browserstack.com/automate/sessions/${sessionId}.json"
        HttpPut putRequest = new HttpPut(new URI(reportUrl))

        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>()
        nameValuePairs.add((new BasicNameValuePair("status", "failed")))
        nameValuePairs.add((new BasicNameValuePair("reason", error.error.toString())))
        putRequest.setEntity(new UrlEncodedFormEntity(nameValuePairs))

        print "Reporting failed test to browserStack with sessionId ${sessionId}"
        HttpClientBuilder.create().build().execute(putRequest)
    }
}

GetConfig.groovy

 /// ...
    browserStack {
        driver = {
            def driver = browserStackDriver()
            BrowserInstance.instance.driver = driver
            return driver
        }
    }