Fix Path.size() and add test for Path.size().

src/main/org/insa/graph/Path.java

@@ -176,7 +176,7 @@ public class Path {
      * @return Number of nodes in this path.
      */
     public int size() {
-        return 1 + this.arcs.size();
+        return isEmpty() ? 0 : 1 + this.arcs.size();
     }
 
     /**

src/test/org/insa/graph/PathTest.java

@@ -93,6 +93,16 @@ public class PathTest {
         assertFalse(longLoopPath.isEmpty());
         assertFalse(invalidPath.isEmpty());
     }
+    
+    @Test
+    public void testSize() {
+        assertEquals(emptyPath.size(), 0);
+        assertEquals(singleNodePath.size(), 1);
+        assertEquals(shortPath.size(), 4);
+        assertEquals(longPath.size(), 5);
+        assertEquals(loopPath.size(), 5);
+        assertEquals(longLoopPath.size(), 10);
+    }
 
     @Test
     public void testIsValid() {