spark + sbt-assembly: "deduplicate: different file contents found in the following"

Question

I ran spark application and wanna pack the test classes into the fat jar. What is weird is I ran "sbt assembly" successfully, but failed when I ran "sbt test:assembly".

I tried sbt-assembly : including test classes, it didn't work for my case.

SBT version : 0.13.8

build.sbt:

import sbtassembly.AssemblyPlugin._

name := "assembly-test"

version := "1.0"

scalaVersion := "2.10.5"

libraryDependencies ++= Seq(
  ("org.apache.spark" % "spark-core_2.10" % "1.3.1" % Provided)
    .exclude("org.mortbay.jetty", "servlet-api").
    exclude("commons-beanutils", "commons-beanutils-core").
    exclude("commons-collections", "commons-collections").
    exclude("commons-logging", "commons-logging").
    exclude("com.esotericsoftware.minlog", "minlog").exclude("com.codahale.metrics", "metrics-core"),
  "org.json4s" % "json4s-jackson_2.10" % "3.2.10" % Provided,
  "com.google.inject" % "guice" % "4.0"
)

Project.inConfig(Test)(assemblySettings)

Answer 1

As an addition to Wesley Milano's answer, the code needs to be adapted a bit for the newer version (i.e. 0.13.0) of the sbt-assembly plugin, in case someone is wondering about deprecation warnings:

assemblyMergeStrategy in assembly := {
    case PathList("javax", "servlet", xs @ _*) => MergeStrategy.last
    case PathList("javax", "activation", xs @ _*) => MergeStrategy.last
    case PathList("org", "apache", xs @ _*) => MergeStrategy.last
    case PathList("com", "google", xs @ _*) => MergeStrategy.last
    case PathList("com", "esotericsoftware", xs @ _*) => MergeStrategy.last
    case PathList("com", "codahale", xs @ _*) => MergeStrategy.last
    case PathList("com", "yammer", xs @ _*) => MergeStrategy.last
    case "about.html" => MergeStrategy.rename
    case "META-INF/ECLIPSEF.RSA" => MergeStrategy.last
    case "META-INF/mailcap" => MergeStrategy.last
    case "META-INF/mimetypes.default" => MergeStrategy.last
    case "plugin.properties" => MergeStrategy.last
    case "log4j.properties" => MergeStrategy.last
    case x =>
        val oldStrategy = (assemblyMergeStrategy in assembly).value
        oldStrategy(x)
}