test: add DijkstraPriorityQueue tests; format imports

Author: SUZUB

src/main/java/com/thealgorithms/others/Dijkstra.java

@@ -1,9 +1,10 @@
 package com.thealgorithms.others;
 
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.PriorityQueue;
-import java.util.Comparator;
+
 /**
  * Dijkstra's algorithm,is a graph search algorithm that solves the
  * single-source shortest path problem for a graph with nonnegative edge path

src/test/java/com/thealgorithms/graphs/DijkstraPriorityQueueTest.java

@@ -0,0 +1,65 @@
+package com.thealgorithms.graphs;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+/**
+ * Unit tests for {@link DijkstraPriorityQueue}.
+ */
+public class DijkstraPriorityQueueTest {
+
+    private DijkstraPriorityQueue dijkstra;
+
+    @BeforeEach
+    void setUp() {
+        dijkstra = new DijkstraPriorityQueue();
+    }
+
+    @Test
+    void testSimpleGraph() {
+        Map<Integer, List<DijkstraPriorityQueue.Edge>> graph = new HashMap<>();
+        graph.put(0, List.of(new DijkstraPriorityQueue.Edge(1, 7), new DijkstraPriorityQueue.Edge(2, 9)));
+        graph.put(1, List.of(new DijkstraPriorityQueue.Edge(2, 10)));
+        graph.put(2, new ArrayList<>());
+
+        int[] result = dijkstra.runDijkstra(0, graph, 3);
+        int[] expected = {0, 7, 9};
+        assertArrayEquals(expected, result);
+    }
+
+    @Test
+    void testNegativeWeightThrows() {
+        Map<Integer, List<DijkstraPriorityQueue.Edge>> graph = new HashMap<>();
+        graph.put(0, List.of(new DijkstraPriorityQueue.Edge(1, -1)));
+        graph.put(1, new ArrayList<>());
+
+        assertThrows(IllegalArgumentException.class, () -> dijkstra.runDijkstra(0, graph, 2));
+    }
+
+    @Test
+    void testDisconnectedGraph() {
+        Map<Integer, List<DijkstraPriorityQueue.Edge>> graph = new HashMap<>();
+        graph.put(0, new ArrayList<>());
+        graph.put(1, new ArrayList<>());
+
+        int[] result = dijkstra.runDijkstra(0, graph, 2);
+        int[] expected = {0, Integer.MAX_VALUE};
+        assertArrayEquals(expected, result);
+    }
+
+    @Test
+    void testEmptyGraph() {
+        Map<Integer, List<DijkstraPriorityQueue.Edge>> graph = new HashMap<>();
+        int[] result = dijkstra.runDijkstra(0, graph, 0);
+        int[] expected = {};
+        assertArrayEquals(expected, result);
+    }
+}