Block Edge Weight Modification in Unmodifiable View (#1217)

* Block edge weight modification in unmodifiable view

* Add tests for unmodiable view

jgrapht-core/src/main/java/org/jgrapht/graph/AsUnmodifiableGraph.java

@@ -157,4 +157,24 @@ public GraphType getType()
     {
         return super.getType().asUnmodifiable();
     }
+
+    /**
+     * @throws UnsupportedOperationException always
+     * 
+     * @since 1.5.3
+     */
+    @Override
+    public void setEdgeWeight(E e, double weight) {
+        throw new UnsupportedOperationException(UNMODIFIABLE);
+    }
+
+    /**
+     * @throws UnsupportedOperationException always
+     * 
+     * @since 1.5.3
+     */
+    @Override
+    public void setEdgeWeight(V sourceVertex, V targetVertex, double weight) {
+        throw new UnsupportedOperationException(UNMODIFIABLE);
+    }
 }

jgrapht-core/src/test/java/org/jgrapht/graph/AsUnmodifiableGraphTest.java

@@ -0,0 +1,90 @@
+/*
+ * (C) Copyright 2024-2024, by Sung Ho Yoon and Contributors.
+ *
+ * JGraphT : a free Java graph-theory library
+ *
+ * See the CONTRIBUTORS.md file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0, or the
+ * GNU Lesser General Public License v2.1 or later
+ * which is available at
+ * http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
+ */
+package org.jgrapht.graph;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.jgrapht.*;
+import org.junit.jupiter.api.*;
+
+@DisplayName("Unmodifiable graph view tests")
+public class AsUnmodifiableGraphTest {
+
+    private DefaultWeightedEdge loop;
+    private DefaultWeightedEdge e12;
+    private DefaultWeightedEdge e23;
+    private DefaultWeightedEdge e24;
+    private String v1 = "v1";
+    private String v2 = "v2";
+    private String v3 = "v3";
+    private String v4 = "v4";
+    private Graph<String, DefaultWeightedEdge> baseGraph;
+    private Graph<String, DefaultWeightedEdge> unmodifiableGraph;
+
+    @BeforeEach
+    public void setUp()
+    {
+        this.baseGraph =
+            new DefaultUndirectedWeightedGraph<>(DefaultWeightedEdge.class);
+
+        baseGraph.addVertex(v1);
+        baseGraph.addVertex(v2);
+        baseGraph.addVertex(v3);
+        baseGraph.addVertex(v4);
+        e12 = Graphs.addEdge(baseGraph, v1, v2, 6d);
+        e23 = Graphs.addEdge(baseGraph, v2, v3, 456d);
+        e24 = Graphs.addEdge(baseGraph, v2, v4, 0.587d);
+        loop = Graphs.addEdge(baseGraph, v4, v4, 6781234453486d);
+
+        this.unmodifiableGraph = new AsUnmodifiableGraph<>(this.baseGraph);
+    }
+
+    @DisplayName("Test null graph")
+    @Test
+    public void testNullGraph() {
+        assertThrows(NullPointerException.class, () -> new AsUnmodifiableGraph<>(null));
+    }
+
+    @DisplayName("Test edge addition")
+    @Test
+    public void testAddEdge()
+    {
+        assertThrows(UnsupportedOperationException.class, () -> unmodifiableGraph.addEdge(v3, v4));
+        assertThrows(UnsupportedOperationException.class, () -> {
+            DefaultWeightedEdge e34 = new DefaultWeightedEdge();
+            e34.source = v3;
+            e34.target = v4;
+            e34.weight = 2d;
+            unmodifiableGraph.addEdge(v3, v4, e34);
+        });
+    }
+
+    @DisplayName("Test vertex addition")
+    @Test
+    public void testAddVertex() {
+        assertThrows(UnsupportedOperationException.class, () -> unmodifiableGraph.addVertex());
+        assertThrows(UnsupportedOperationException.class, () -> unmodifiableGraph.addVertex("v5"));
+    }
+
+    @DisplayName("Test edge weight modification")
+    @Test
+    public void testSetEdgeWeight() {
+        assertThrows(UnsupportedOperationException.class, () -> unmodifiableGraph.setEdgeWeight(v1, v2, 0d));
+        assertEquals(6d, baseGraph.getEdgeWeight(e12));
+    }
+}