SearchServices behaves different from other NamespaceManager compatible services such as MemcacheServices and DatastoreServices. After a NamaespaceManager.set() invocation its necessary to obtain a new SearchService instance from SearchServiceFactory. http://stackoverflow.com/questions/11019473/change-namespacemanager-on-full-text-search-gae

GaeNamespaceManagerTests.java

package com.ciandt.d1.commons.cloud;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNull;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import com.google.appengine.api.NamespaceManager;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.memcache.MemcacheService;
import com.google.appengine.api.memcache.MemcacheServiceFactory;
import com.google.appengine.api.search.Document;
import com.google.appengine.api.search.Field;
import com.google.appengine.api.search.IndexSpec;
import com.google.appengine.api.search.SearchService;
import com.google.appengine.api.search.SearchServiceFactory;
import com.google.appengine.tools.development.testing.LocalDatastoreServiceTestConfig;
import com.google.appengine.tools.development.testing.LocalMemcacheServiceTestConfig;
import com.google.appengine.tools.development.testing.LocalServiceTestHelper;

public class GaeNamespaceManagerTests {

    private static final String EMPTY = "";

    private static final String TWO = "--two--";

    final LocalServiceTestHelper helper = new LocalServiceTestHelper(new LocalDatastoreServiceTestConfig(),
            new LocalMemcacheServiceTestConfig());

    @Before
    public void setup() throws Exception {
        helper.setUp();
    }
    
    @Test
    public void testSearchService() {
        SearchService searchService = SearchServiceFactory.getSearchService();
        searchService.getIndex(indexSpec()).put(document());
        NamespaceManager.set(TWO);
        assertNull(searchService.getIndex(indexSpec()).get("123456")); //fails
        
        NamespaceManager.set(EMPTY);
        assertEquals("123456",searchService.getIndex(indexSpec()).get("123456").getId());
    }

    private Document document() {
        return Document.newBuilder()
        .addField(Field.newBuilder().setName("myField").setText("myFieldValue"))
                .setId("123456").build();
    }
    
    private IndexSpec indexSpec() {
        return IndexSpec.newBuilder().setName("MyIndex").build();
    }
    
    @Test
    public void testMemcacheService() {
        MemcacheService memcacheService = MemcacheServiceFactory.getMemcacheService();
        memcacheService.put("mykey", "myobj");
        NamespaceManager.set(TWO);
        assertNull(memcacheService.get("mykey"));
        NamespaceManager.set(EMPTY);
        assertEquals("myobj", memcacheService.get("mykey"));
    }
    
    @Test
    public void testDatastoreService()  {
        DatastoreService datastoreService = DatastoreServiceFactory.getDatastoreService();
        Entity entity = new Entity("MyKind", 1l);
        datastoreService.put(entity);

        NamespaceManager.set(TWO);
        try {
            datastoreService.get(KeyFactory.createKey("MyKind", 1l));
            Assert.fail();
        } catch (EntityNotFoundException e) {
        }
        
        NamespaceManager.set(EMPTY);
        try {
            datastoreService.get(KeyFactory.createKey("MyKind", 1l));
        } catch (EntityNotFoundException e) {
            Assert.fail();
        }
    }

}