Adding an Asset to already existing ArchivePath is silently ignored

import java.io.IOException;
import java.io.InputStream;
import java.io.StringWriter;

import junit.framework.Assert;

import org.apache.commons.io.IOUtils;
import org.jboss.shrinkwrap.api.Archive;
import org.jboss.shrinkwrap.api.ArchivePath;
import org.jboss.shrinkwrap.api.ArchivePaths;
import org.jboss.shrinkwrap.api.ShrinkWrap;
import org.jboss.shrinkwrap.api.asset.StringAsset;
import org.jboss.shrinkwrap.api.spec.JavaArchive;
import org.junit.Test;

public class SimpleTest {

    @Test
    // fails
    public void simple() throws Exception {
        JavaArchive jar = ShrinkWrap.create(JavaArchive.class)
                .add(new StringAsset("foo"), ArchivePaths.create("resources/foo"))
                .add(new StringAsset("bar"), ArchivePaths.create("resources/foo"));

        // here it should either fail fast before or contain bar
        Assert.assertEquals("Expecting bar", "bar", getContent(jar, ArchivePaths.create("resources/foo")));
    }

    @Test
    // fails
    public void mergeJar1Jar2() throws Exception {
        JavaArchive jar1 = ShrinkWrap.create(JavaArchive.class).add(new StringAsset("foo"),
                ArchivePaths.create("resources/foo"));

        JavaArchive jar2 = ShrinkWrap.create(JavaArchive.class).add(new StringAsset("bar"),
                ArchivePaths.create("resources/foo"));

        JavaArchive jar = jar1.merge(jar2);

        // here it should either fail or contain bar
        Assert.assertEquals("Expecting bar", "bar", getContent(jar, ArchivePaths.create("resources/foo")));
    }

    @Test
    // passes
    public void mergeJar2Jar1() throws Exception {
        JavaArchive jar1 = ShrinkWrap.create(JavaArchive.class).add(new StringAsset("foo"),
                ArchivePaths.create("resources/foo"));

        JavaArchive jar2 = ShrinkWrap.create(JavaArchive.class).add(new StringAsset("bar"),
                ArchivePaths.create("resources/foo"));

        JavaArchive jar = jar2.merge(jar1);

        // here it should either fail or contain bar
        Assert.assertEquals("Expecting bar", "bar", getContent(jar, ArchivePaths.create("resources/foo")));
    }

    private String getContent(Archive<?> archive, ArchivePath path) throws IOException {
        InputStream is = archive.get(path).getAsset().openStream();
        StringWriter w = new StringWriter();
        IOUtils.copy(is, w);
        IOUtils.closeQuietly(is);
        IOUtils.closeQuietly(w);

        return w.toString();
    }
}