A way of testing closures in Grails

MyController.groovy

def action() {
        mailService.sendMail emailParameters(params.mailTo, params.subject, params.body, attachments)
}

protected Closure emailParameters(List<String> mailTo, String mailSubject, String mailBody, List attachments) {
	return {
		multipart true
		to mailTo
		subject mailSubject
		body mailBody
		attachments.each {
			attachBytes (it.filename, it.mime, it.bytes)
		}
	} as Closure
}

MyControllerSpec.groovy

def ".emailParameters creates a configuration closure with the right properties set"() {
	given:
		def closure = controller.emailParameters(emailTo, emailSubject, emailBody, attachments)
		def closureDelegate = Mock(Closure)
		closure.delegate = closureDelegate
		
	when:
		closure()
	
	then:
		1*closureDelegate.invokeMethod('multipart', [true])
		
	where:
		emailBody = "body"
		emailSubject = "subject"
		emailTo = ["somebody@example.org"]
		attachments = []
}