add and test helper to easily get random routes and jobs from collection

jsprit-core/src/main/java/jsprit/core/util/RandomUtils.java

@@ -12,20 +12,18 @@ import java.util.Random;
 public class RandomUtils {
 
     public static VehicleRoute nextRoute(Collection<VehicleRoute> routes, Random random){
-        int randomIndex = random.nextInt(routes.size());
+        return nextItem(routes,random);
-        int count = 0;
-        for(VehicleRoute route : routes){
-            if(count <= randomIndex) return route;
-            count++;
-        }
-        return null;
     }
 
     public static Job nextJob(Collection<Job> jobs, Random random){
-        int randomIndex = random.nextInt(jobs.size());
+        return nextItem(jobs,random);
+    }
+
+    public static <T> T nextItem(Collection<T> items, Random random){
+        int randomIndex = random.nextInt(items.size());
         int count = 0;
-        for(Job job : jobs){
+        for(T item : items){
-            if(count <= randomIndex) return job;
+            if(count == randomIndex) return item;
             count++;
         }
         return null;

jsprit-core/src/test/java/jsprit/core/util/RandomUtilsTest.java

@@ -0,0 +1,44 @@
+package jsprit.core.util;
+
+import jsprit.core.problem.job.Job;
+import junit.framework.Assert;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.List;
+import java.util.Random;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+/**
+ * Created by schroeder on 14/01/15.
+ */
+public class RandomUtilsTest {
+
+    @Test
+    public void shouldReturnSingleJob(){
+        Job job = mock(Job.class);
+        Collection<Job> jobs = Arrays.asList(job);
+        Assert.assertEquals(job, RandomUtils.nextItem(jobs, RandomNumberGeneration.getRandom()));
+    }
+
+    @Test
+    public void shouldReturnSingleJob_(){
+        Job job = mock(Job.class);
+        Collection<Job> jobs = Arrays.asList(job);
+        Assert.assertEquals(job, RandomUtils.nextJob(jobs, RandomNumberGeneration.getRandom()));
+    }
+
+    @Test
+    public void shouldReturnJob3(){
+        Job job3 = mock(Job.class);
+        List<Job> jobs = Arrays.asList(mock(Job.class),mock(Job.class),job3);
+        Random random = mock(Random.class);
+        when(random.nextInt(jobs.size())).thenReturn(2);
+        Assert.assertEquals(job3,RandomUtils.nextJob(jobs,random));
+    }
+
+
+}