geb.Browser is trying to use FirefoxDriver instead of PhatomJSDriver

For some reason, my code tries to use the firefox browser when it should be using phantomjs.

My groovy code looks like this:

import geb.Browser
...

env = System.getenv()    
def username = env.username
def password = env.password
def gateway = env.gateway

def matcher = gateway =~ /^(https?:\/\/)([^:^\/]*)(:\d*)?(.*)?.*$/
def host = matcher[0][2]
def port = matcher[0][3]

if (env.driver == 'firefox') {
    driver = new FirefoxDriver()
} else {
    println env.phantomjspath
    def caps = DesiredCapabilities.phantomjs()
    caps.setCapability(
        PhantomJSDriverService.PHANTOMJS_EXECUTABLE_PATH_PROPERTY, env.phantomjspath
        )
    driver = new PhantomJSDriver(caps)
    driver.manage().window().setSize(new Dimension(1028, 768))
}

def browser = new Browser(driver: driver)

BiHome = "https://" + username + ":" + password + "@" + host + port + "/gateway/default/BigInsightsWeb/#/welcome"

browser.drive {
    go BiHome
    //  code omitted for brevity
}
browser.close()

Unfortunately, for some reason geb.Browser is trying to use the FirefoxDriver:

:CheckHomePhantomJS
/Users/snowch/Repos/biginsight-examples2/examples/BiginsightsHome/build/webdriver/phantomjs/bin/phantomjs
May 10, 2016 10:13:57 AM org.openqa.selenium.phantomjs.PhantomJSDriverService <init>
INFO: executable: /Users/snowch/Repos/biginsight-examples2/examples/BiginsightsHome/build/webdriver/phantomjs/bin/phantomjs
May 10, 2016 10:13:57 AM org.openqa.selenium.phantomjs.PhantomJSDriverService <init>
INFO: port: 19084
May 10, 2016 10:13:57 AM org.openqa.selenium.phantomjs.PhantomJSDriverService <init>
INFO: arguments: [--webdriver=19084, --webdriver-logfile=/Users/snowch/Repos/biginsight-examples2/examples/BiginsightsHome/phantomjsdriver.log]
May 10, 2016 10:13:57 AM org.openqa.selenium.phantomjs.PhantomJSDriverService <init>
INFO: environment: {}
PhantomJS is launching GhostDriver...
[INFO  - 2016-05-10T09:13:58.925Z] GhostDriver - Main - running on port 19084
[INFO  - 2016-05-10T09:13:59.117Z] Session [8784a390-168f-11e6-bcd7-a7a5f8e205b1] - page.settings - {"XSSAuditingEnabled":false,"javascriptCanCloseWindows":true,"javascriptCanOpenWindows":true,"javascriptEnabled":true,"loadImages":true,"localToRemoteUrlAccessEnabled":false,"userAgent":"Mozilla/5.0 (Macintosh; Intel Mac OS X) AppleWebKit/534.34 (KHTML, like Gecko) PhantomJS/1.9.7 Safari/534.34","webSecurityEnabled":true}
[INFO  - 2016-05-10T09:13:59.117Z] Session [8784a390-168f-11e6-bcd7-a7a5f8e205b1] - page.customHeaders:  - {}
[INFO  - 2016-05-10T09:13:59.117Z] Session [8784a390-168f-11e6-bcd7-a7a5f8e205b1] - Session.negotiatedCapabilities - {"browserName":"phantomjs","version":"1.9.7","driverName":"ghostdriver","driverVersion":"1.1.0","platform":"mac-unknown-32bit","javascriptEnabled":true,"takesScreenshot":true,"handlesAlerts":false,"databaseEnabled":false,"locationContextEnabled":false,"applicationCacheEnabled":false,"browserConnectionEnabled":false,"cssSelectorsEnabled":true,"webStorageEnabled":false,"rotatable":false,"acceptSslCerts":false,"nativeEvents":true,"proxy":{"proxyType":"direct"}}
[INFO  - 2016-05-10T09:13:59.117Z] SessionManagerReqHand - _postNewSessionCommand - New Session Created: 8784a390-168f-11e6-bcd7-a7a5f8e205b1
Exception in thread "main" org.openqa.selenium.WebDriverException: Cannot find firefox binary in PATH. Make sure firefox is installed. OS appears to be: MAC
Build info: version: '2.53.0', revision: '35ae25b1534ae328c771e0856c93e187490ca824', time: '2016-03-15 10:43:46'
System info: host: 'xxxxxxx', ip: 'xxxxx', os.name: 'Mac OS X', os.arch: 'x86_64', os.version: 'xxxxx', java.version: '1.8.0_66'
Driver info: driver.version: FirefoxDriver
    at org.openqa.selenium.firefox.internal.Executable.<init>(Executable.java:75)
    at org.openqa.selenium.firefox.FirefoxBinary.<init>(FirefoxBinary.java:60)
    at org.openqa.selenium.firefox.FirefoxBinary.<init>(FirefoxBinary.java:56)
    at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:120)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    ....

My build.gradle:

import org.apache.tools.ant.taskdefs.condition.Os

// set the dependencies for running the groovy script
buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'org.codehaus.groovy:groovy-all:latest.release'
    }
}

plugins {
  id 'groovy'
}

apply from: "osSpecificDownloads.gradle"

// set the dependencies for compiling the groovy script
repositories {
    mavenCentral()
}

dependencies {
    compile 'org.codehaus.groovy:groovy-all:latest.release'
    compile 'org.codehaus.geb:geb-core:latest.release'
    compile 'org.seleniumhq.selenium:selenium-firefox-driver:2.53.0'
    compile('com.codeborne:phantomjsdriver:1.3.0') {
        transitive = false
    }
}

// tell gradle the groovy script is in the same folder as the build.gradle file
sourceSets {
    main {
        groovy {
            srcDirs = ['.']
        }
    }
}

Properties props = new Properties()
props.load(new FileInputStream("$projectDir/../../connection.properties"))

task("CheckHomePhantomJS", type: JavaExec) {

    dependsOn unzipPhantomJs

    def phantomJsFilename = Os.isFamily(Os.FAMILY_WINDOWS) ? "phantomjs.exe" : "bin/phantomjs"

    environment 'phantomjspath', new File(unzipPhantomJs.outputs.files.singleFile, phantomJsFilename).absolutePath
    environment 'driver', 'phantomjs'

    environment 'gateway', props.gateway
    environment 'username', props.username
    environment 'password', props.password

    main = 'CheckHome'
    classpath = sourceSets.main.runtimeClasspath
}

Any idea what is going wrong here?

Geb creates a new Browser instance when you call.

Browser drive(Closure script) 

Instead try with

Browser drive(Browser browser, Closure script)

So change your code to

Browser.drive(browser) {
    go BiHome
    //  code omitted for brevity
}