Depending on Project Dependency Shadow Jar

client.gradle

// Client subproject build file - client/build.gradle
apply plugin: 'java'
apply plugin: 'com.github.johnrengelman.shadow'

repositories {
  jcenter()
}

dependencies {
  compile 'junit:junit:3.8.2'
}

shadowJar {
  relocate 'junit.framework', 'client.junit.framework'
}

server.gradle

// Server subproject build file - server/build.gradle
apply plugin: 'java'
apply plugin: 'com.github.johnrengelman.shadow'

repositories {
  jcenter()
}

dependencies {
  // add compile & runtime dependencies
  compile project(path: ':client', configuration: 'shadow')
}

ServerTest.groovy

//This file would be in the :server subproject - server/src/main/groovy/server/ServerTest.groovy
package server

imort client.junit.framework.Test

interface ServerTest extends Test {}