Add a test case for externalizable

src/test/java/net/openhft/chronicle/map/externalizable/ExternalizableTest.java

@@ -0,0 +1,32 @@
+package net.openhft.chronicle.map.externalizable;
+
+import net.openhft.chronicle.core.OS;
+import net.openhft.chronicle.map.ChronicleMap;
+import net.openhft.chronicle.map.ChronicleMapBuilder;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+
+public class ExternalizableTest {
+    @Test
+    public void externalizable() throws IOException {
+        String path = OS.TARGET + "/test-" + System.nanoTime() + ".map";
+        new File(path).deleteOnExit();
+        try (ChronicleMap<Long, SomeClass> storage = ChronicleMapBuilder
+                .of(Long.class, SomeClass.class)
+                .averageValueSize(128)
+                .entries(128)
+                .createPersistedTo(new File(path))) {
+            SomeClass value = new SomeClass();
+            value.hits.add("one");
+            value.hits.add("two");
+            storage.put(1L, value);
+
+            SomeClass value2 = storage.get(1L);
+            assertEquals(value.hits, value2.hits);
+        }
+    }
+}

src/test/java/net/openhft/chronicle/map/externalizable/SomeClass.java

@@ -0,0 +1,32 @@
+package net.openhft.chronicle.map.externalizable;
+
+import java.io.Externalizable;
+import java.io.IOException;
+import java.io.ObjectInput;
+import java.io.ObjectOutput;
+import java.util.ArrayList;
+import java.util.List;
+
+public class SomeClass implements Externalizable {
+
+    final List<String> hits = new ArrayList<>();
+    private long id;
+
+    @Override
+    public void writeExternal(ObjectOutput out) throws IOException {
+        out.writeLong(id);
+        out.writeInt(hits.size());
+        for (int i = 0; i < hits.size(); i++) {
+            out.writeObject(hits.get(i));
+        }
+    }
+
+    @Override
+    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
+        id = in.readLong();
+        int size = in.readInt();
+        for (int i = 0; i < size; i++) {
+            hits.add((String) in.readObject());
+        }
+    }
+}