Removed graphsearch folder and added additional unit tests for TopologicalSort

Author: Saipatnaik-23

src/test/java/com/thealgorithms/sorts/TopologicalSortTest.java

@@ -1,12 +1,14 @@
 package com.thealgorithms.sorts;
 
+import com.thealgorithms.sorts.TopologicalSort.Graph;
+import java.util.LinkedList;
+import org.junit.jupiter.api.Test;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertIterableEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import com.thealgorithms.sorts.TopologicalSort.Graph;
-import java.util.LinkedList;
-import org.junit.jupiter.api.Test;
 
 class TopologicalSortTest {
 
@@ -59,4 +61,18 @@ public void failureTest() {
             + "Back edge: 6 -> 2";
         assertEquals(exception.getMessage(), expected);
     }
+    @Test
+    void testEmptyGraph() {
+        Graph graph = new Graph();
+        LinkedList<String> sorted = TopologicalSort.sort(graph);
+        assertTrue(sorted.isEmpty());
+    }
+    @Test
+    void testSingleNode() {
+        Graph graph = new Graph();
+        graph.addEdge("A", "");
+        LinkedList<String> sorted = TopologicalSort.sort(graph);
+        assertEquals(1, sorted.size());
+        assertEquals("A", sorted.getFirst());
+    }
 }