Now, i hava a method defined like below:

public final class StringUtils {

    public static String format(String format, Object... args) {
         // do sth.
    }

}

and my spock tests code like this:

class StringUtilsTests extends Specification {

    def "format: normal"() {
        given:
        def messageFormat = "test {}, {}"
        def args = ["message", "format"]

        when:

        def message = StringUtils.format(messageFormat, "message", "format")
        def message2 = StringUtils.format(messageFormat, args)
        def message3 = StringUtils.format(messageFormat, args as Object[])
        def message4 = StringUtils.format(messageFormat, args.flatten)

        then:
        message == "test message, format"
        message2 == "test message, format"
        message3 == "test message, format"
        message4 == "test message, format"
    }
}

All of result is test ["message", "format"], {}

so, how to call a java vararg method with spock?