test: NQueensTest (#5378)

Author: alxkm

src/main/java/com/thealgorithms/backtracking/NQueens.java

@@ -36,13 +36,10 @@ public final class NQueens {
     private NQueens() {
     }
 
-    public static void main(String[] args) {
-        placeQueens(1);
-        placeQueens(2);
-        placeQueens(3);
-        placeQueens(4);
-        placeQueens(5);
-        placeQueens(6);
+    public static List<List<String>> getNQueensArrangements(int queens) {
+        List<List<String>> arrangements = new ArrayList<>();
+        getSolution(queens, arrangements, new int[queens], 0);
+        return arrangements;
     }
 
     public static void placeQueens(final int queens) {

src/test/java/com/thealgorithms/backtracking/NQueensTest.java

@@ -0,0 +1,48 @@
+package com.thealgorithms.backtracking;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+public class NQueensTest {
+
+    @Test
+    public void testNQueens1() {
+        List<List<String>> expected = Arrays.asList(Arrays.asList("Q"));
+        assertEquals(expected, NQueens.getNQueensArrangements(1));
+    }
+
+    @Test
+    public void testNQueens2() {
+        List<List<String>> expected = new ArrayList<>(); // No solution exists
+        assertEquals(expected, NQueens.getNQueensArrangements(2));
+    }
+
+    @Test
+    public void testNQueens3() {
+        List<List<String>> expected = new ArrayList<>(); // No solution exists
+        assertEquals(expected, NQueens.getNQueensArrangements(3));
+    }
+
+    @Test
+    public void testNQueens4() {
+        List<List<String>> expected = Arrays.asList(Arrays.asList(".Q..", "...Q", "Q...", "..Q."), Arrays.asList("..Q.", "Q...", "...Q", ".Q.."));
+        assertEquals(expected, NQueens.getNQueensArrangements(4));
+    }
+
+    @Test
+    public void testNQueens5() {
+        // Only the number of solutions is tested for larger N due to the complexity of checking each board configuration
+        List<List<String>> result = NQueens.getNQueensArrangements(5);
+        assertEquals(10, result.size()); // 5x5 board has 10 solutions
+    }
+
+    @Test
+    public void testNQueens6() {
+        List<List<String>> result = NQueens.getNQueensArrangements(6);
+        assertEquals(4, result.size()); // 6x6 board has 4 solutions
+    }
+}