Add tests, enhance class & function documentation for KnightsTour (#5591)

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

@@ -0,0 +1,59 @@
+package com.thealgorithms.backtracking;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class KnightsTourTest {
+
+    @BeforeEach
+    void setUp() {
+        // Call the reset method in the KnightsTour class
+        KnightsTour.resetBoard();
+    }
+
+    @Test
+    void testGridInitialization() {
+        for (int r = 0; r < 12; r++) {
+            for (int c = 0; c < 12; c++) {
+                if (r < 2 || r > 12 - 3 || c < 2 || c > 12 - 3) {
+                    assertEquals(-1, KnightsTour.grid[r][c], "Border cells should be -1");
+                } else {
+                    assertEquals(0, KnightsTour.grid[r][c], "Internal cells should be 0");
+                }
+            }
+        }
+    }
+
+    @Test
+    void testCountNeighbors() {
+        // Manually place a knight at (3, 3) and mark nearby cells to test counting
+        KnightsTour.grid[3][3] = 1; // Knight is here
+        KnightsTour.grid[5][4] = -1; // Block one potential move
+
+        int neighborCount = KnightsTour.countNeighbors(3, 3);
+        assertEquals(3, neighborCount, "Knight at (3, 3) should have 3 neighbors (one blocked)");
+
+        KnightsTour.grid[4][1] = -1; // Block another move
+        neighborCount = KnightsTour.countNeighbors(3, 3);
+        assertEquals(3, neighborCount, "Knight at (3, 3) should have 3 neighbors (two blocked)");
+    }
+
+    @Test
+    void testNeighbors() {
+        // Test the list of valid neighbors for a given cell (3, 3)
+        List<int[]> neighbors = KnightsTour.neighbors(3, 3);
+        assertEquals(4, neighbors.size(), "Knight at (3, 3) should have 8 valid neighbors");
+    }
+
+    @Test
+    void testSolveSuccessful() {
+        // Test if the solve method works for a successful knight's tour
+        KnightsTour.grid[2][2] = 1; // Start the knight at (2, 2)
+        boolean result = KnightsTour.solve(2, 2, 2);
+        assertTrue(result, "solve() should successfully complete a Knight's tour");
+    }
+}