KaprekarNumbersTest.java

package com.thealgorithms.maths;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.util.Arrays;
import java.util.List;
import org.junit.jupiter.api.Test;

/**
 * Test class for {@link KaprekarNumbers}.
 * Tests various Kaprekar numbers and edge cases to ensure full coverage.
 */
class KaprekarNumbersTest {

 @Test
 void testZeroIsKaprekarNumber() {
 assertTrue(KaprekarNumbers.isKaprekarNumber(0));
 }

 @Test
 void testOneIsKaprekarNumber() {
 assertTrue(KaprekarNumbers.isKaprekarNumber(1));
 }

 @Test
 void testNineIsKaprekarNumber() {
 // 9^2 = 81, 8 + 1 = 9
 assertTrue(KaprekarNumbers.isKaprekarNumber(9));
 }

 @Test
 void testFortyFiveIsKaprekarNumber() {
 // 45^2 = 2025, 20 + 25 = 45
 assertTrue(KaprekarNumbers.isKaprekarNumber(45));
 }

 @Test
 void testFiftyFiveIsKaprekarNumber() {
 // 55^2 = 3025, 30 + 25 = 55
 assertTrue(KaprekarNumbers.isKaprekarNumber(55));
 }

 @Test
 void testNinetyNineIsKaprekarNumber() {
 // 99^2 = 9801, 98 + 01 = 99
 assertTrue(KaprekarNumbers.isKaprekarNumber(99));
 }

 @Test
 void testTwoNinetySevenIsKaprekarNumber() {
 // 297^2 = 88209, 88 + 209 = 297
 assertTrue(KaprekarNumbers.isKaprekarNumber(297));
 }

 @Test
 void testSevenZeroThreeIsKaprekarNumber() {
 // 703^2 = 494209, 494 + 209 = 703
 assertTrue(KaprekarNumbers.isKaprekarNumber(703));
 }

 @Test
 void testNineNineNineIsKaprekarNumber() {
 // 999^2 = 998001, 998 + 001 = 999
 assertTrue(KaprekarNumbers.isKaprekarNumber(999));
 }

 @Test
 void testTwoTwoTwoThreeIsKaprekarNumber() {
 // 2223^2 = 4941729, 4941 + 729 = 5670 (not directly obvious)
 // Actually: 494 + 1729 = 2223
 assertTrue(KaprekarNumbers.isKaprekarNumber(2223));
 }

 @Test
 void testEightFiveSevenOneFortyThreeIsKaprekarNumber() {
 assertTrue(KaprekarNumbers.isKaprekarNumber(857143));
 }

 @Test
 void testTwoIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(2));
 }

 @Test
 void testThreeIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(3));
 }

 @Test
 void testTenIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(10));
 }

 @Test
 void testTwentySixIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(26));
 }

 @Test
 void testNinetyEightIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(98));
 }

 @Test
 void testOneHundredIsNotKaprekarNumber() {
 assertFalse(KaprekarNumbers.isKaprekarNumber(100));
 }

 @Test
 void testNegativeNumberThrowsException() {
 assertThrows(IllegalArgumentException.class, () -> KaprekarNumbers.isKaprekarNumber(-5));
 }

 @Test
 void testKaprekarNumbersInSmallRange() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(1, 10);
 List<Long> expected = Arrays.asList(1L, 9L);
 assertEquals(expected, result);
 }

 @Test
 void testKaprekarNumbersInMediumRange() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(1, 100);
 List<Long> expected = Arrays.asList(1L, 9L, 45L, 55L, 99L);
 assertEquals(expected, result);
 }

 @Test
 void testKaprekarNumbersInLargeRange() {
 List<Long> rangedNumbers = KaprekarNumbers.kaprekarNumberInRange(1, 100000);
 List<Long> expectedNumbers = Arrays.asList(1L, 9L, 45L, 55L, 99L, 297L, 703L, 999L, 2223L, 2728L, 4950L, 5050L, 7272L, 7777L, 9999L, 17344L, 22222L, 77778L, 82656L, 95121L, 99999L);
 assertEquals(expectedNumbers, rangedNumbers);
 }

 @Test
 void testKaprekarNumbersInSingleElementRange() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(9, 9);
 List<Long> expected = Arrays.asList(9L);
 assertEquals(expected, result);
 }

 @Test
 void testKaprekarNumbersInRangeWithNoKaprekarNumbers() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(2, 8);
 assertTrue(result.isEmpty());
 }

 @Test
 void testKaprekarNumbersInRangeStartingFromZero() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(0, 5);
 List<Long> expected = Arrays.asList(0L, 1L);
 assertEquals(expected, result);
 }

 @Test
 void testInvalidRangeThrowsException() {
 assertThrows(IllegalArgumentException.class, () -> KaprekarNumbers.kaprekarNumberInRange(100, 50));
 }

 @Test
 void testNegativeStartThrowsException() {
 assertThrows(IllegalArgumentException.class, () -> KaprekarNumbers.kaprekarNumberInRange(-10, 100));
 }

 @Test
 void testEmptyRange() {
 List<Long> result = KaprekarNumbers.kaprekarNumberInRange(10, 44);
 assertTrue(result.isEmpty());
 }

 @Test
 void testLargeKaprekarNumber() {
 // Test a larger known Kaprekar number
 assertTrue(KaprekarNumbers.isKaprekarNumber(142857));
 }

 @Test
 void testFourDigitKaprekarNumbers() {
 // Test some 4-digit Kaprekar numbers
 assertTrue(KaprekarNumbers.isKaprekarNumber(2728));
 assertTrue(KaprekarNumbers.isKaprekarNumber(4950));
 assertTrue(KaprekarNumbers.isKaprekarNumber(5050));
 assertTrue(KaprekarNumbers.isKaprekarNumber(7272));
 }
}