how to pass gradle systemProperties JUnit5 tests

i am using gradle 3.5 and Unit 5 (jupiter).

i wish to pass System property to my tests, in order to configure the test

i am running the test using this command gradle test -Denv=envFile1

here is my grade file :

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'org.junit.platform:junit-platform-gradle-plugin:1.0.0-M4' //JUnit 5
    }
}

repositories {
    mavenCentral()
}   

ext.versionJunitPlatform        = '1.0.0-M4'
ext.versionJunitJupiter         = '5.0.0-M4'
ext.versionLog4j                = '1.2.17'
ext.versionRestAssured          = '2.9.0'
ext.versionRestAssuredJsonValid = '3.0.2'
ext.versionHamcrest             = '1.3'
ext.versionJacksonDatabind      = '2.9.0.pr2'
ext.versionSeleniumJava         = '3.3.1' 

test.systemProperties System.properties

dependencies {
    compile group: 'log4j'                      , name: 'log4j'                 , version: "$versionLog4j"               //Log4j
    compile group: 'com.jayway.restassured'     , name: 'rest-assured'          , version: "$versionRestAssured"         //Rest Assure
    compile group: 'io.rest-assured'            , name: 'json-schema-validator' , version: "$versionRestAssuredJsonValid"     //Rest Assure schema validation
    compile group: 'org.hamcrest'               , name: 'hamcrest-all'          , version: "$versionHamcrest"      //Rest Assure assertion
    compile group: 'com.fasterxml.jackson.core' , name: 'jackson-databind'      , version: "$versionJacksonDatabind" //Serilize/Deserialize Request/Response objects
    compile group: 'org.seleniumhq.selenium'    , name: 'selenium-java'         , version: "$versionSeleniumJava"    //Selenium core, E2E testing

    testCompile group: 'org.junit.jupiter' , name: 'junit-jupiter-api'     , version: "$versionJunitJupiter"
    testRuntime group: 'org.junit.jupiter' , name: 'junit-jupiter-engine'  , version: "$versionJunitJupiter"
}

Here is my test:

package com.somecompany.someProject.tests;

import org.junit.jupiter.api.Test;

public class AaTest {
    @Test
    public void a() {
        System.out.println("a test: " + System.getProperty("env"));
    }
} 

This is the output i get

gradle test -Denv=envName
:compileJava UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:compileTestJava
:processTestResources UP-TO-DATE
:testClasses
:junitPlatformTest
a test: null

thank you

shay