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diff --git a/watchmaker/framework/src/java/test/org/uncommons/watchmaker/framework/operators/StringCrossoverTest.java b/watchmaker/framework/src/java/test/org/uncommons/watchmaker/framework/operators/StringCrossoverTest.java
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+//=============================================================================
+// Copyright 2006-2010 Daniel W. Dyer
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//=============================================================================
+package org.uncommons.watchmaker.framework.operators;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import org.testng.annotations.Test;
+import org.uncommons.maths.random.Probability;
+import org.uncommons.watchmaker.framework.EvolutionaryOperator;
+import org.uncommons.watchmaker.framework.FrameworkTestUtils;
+
+/**
+ * Unit test for cross-over with Strings.
+ * @author Daniel Dyer
+ */
+public class StringCrossoverTest
+{
+    @Test
+    public void testCrossover()
+    {
+        EvolutionaryOperator<String> crossover = new StringCrossover();
+        List<String> population = new ArrayList<String>(4);
+        population.add("abcde");
+        population.add("fghij");
+        population.add("klmno");
+        population.add("pqrst");
+        Set<Character> values = new HashSet<Character>(20);
+        for (int i = 0; i < 20; i++)
+        {
+            population = crossover.apply(population, FrameworkTestUtils.getRNG());
+            assert population.size() == 4 : "Population size changed after cross-over.";
+            for (String individual : population)
+            {
+                assert individual.length() == 5 : "Invalid candidate length: " + individual.length();
+                for (char value : individual.toCharArray())
+                {
+                    values.add(value);
+                }
+            }
+            // All of the individual elements should still be present, just jumbled up
+            // between individuals.
+            assert values.size() == 20 : "Information lost during cross-over.";
+            values.clear();
+        }
+    }
+
+
+    /**
+     * The {@link StringCrossover} operator is only defined to work on populations
+     * containing Strings of equal lengths.  Any attempt to apply the operation to
+     * populations that contain different length Strings should throw an exception.
+     * Not throwing an exception should be considered a bug since it could lead to
+     * hard to trace bugs elsewhere.
+     */
+    @Test(expectedExceptions = IllegalArgumentException.class)
+    public void testDifferentLengthParents()
+    {
+        EvolutionaryOperator<String> crossover = new StringCrossover(1, Probability.ONE);
+        List<String> population = new ArrayList<String>(2);
+        population.add("abcde");
+        population.add("fghijklm");
+        // This should cause an exception since the parents are different lengths.
+        crossover.apply(population, FrameworkTestUtils.getRNG());
+    }
+
+
+    /**
+     * Number of cross-over points must be greater than zero otherwise the operator
+     * is a no-op.
+     */
+    @Test(expectedExceptions = IllegalArgumentException.class)
+    public void testZeroCrossoverPoints()
+    {
+        new StringCrossover(0, Probability.EVENS); // Should throw an IllegalArgumentException.
+    }
+}