Java/src/test/java/com/thealgorithms/maths/HarshadNumberTest.java at master · TheAlgorithms/Java · GitHub

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packagecom.thealgorithms.maths;

importorg.junit.jupiter.api.Assertions;
importorg.junit.jupiter.api.Test;

/**
 * Test class for {@link HarshadNumber}.
 * Tests various scenarios including positive cases, edge cases, and exception
 * handling.
 */
classHarshadNumberTest {

@Test
voidtestValidHarshadNumbers() {
// Single digit Harshad numbers (all single digits except 0 are Harshad numbers)
Assertions.assertTrue(HarshadNumber.isHarshad(1));
Assertions.assertTrue(HarshadNumber.isHarshad(2));
Assertions.assertTrue(HarshadNumber.isHarshad(3));
Assertions.assertTrue(HarshadNumber.isHarshad(4));
Assertions.assertTrue(HarshadNumber.isHarshad(5));
Assertions.assertTrue(HarshadNumber.isHarshad(6));
Assertions.assertTrue(HarshadNumber.isHarshad(7));
Assertions.assertTrue(HarshadNumber.isHarshad(8));
Assertions.assertTrue(HarshadNumber.isHarshad(9));

// Two digit Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad(10)); // 10 / (1 + 0) = 10
Assertions.assertTrue(HarshadNumber.isHarshad(12)); // 12 / (1 + 2) = 4
Assertions.assertTrue(HarshadNumber.isHarshad(18)); // 18 / (1 + 8) = 2
Assertions.assertTrue(HarshadNumber.isHarshad(20)); // 20 / (2 + 0) = 10
Assertions.assertTrue(HarshadNumber.isHarshad(21)); // 21 / (2 + 1) = 7

// Three digit Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad(100)); // 100 / (1 + 0 + 0) = 100
Assertions.assertTrue(HarshadNumber.isHarshad(102)); // 102 / (1 + 0 + 2) = 34
Assertions.assertTrue(HarshadNumber.isHarshad(108)); // 108 / (1 + 0 + 8) = 12

// Large Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad(1000)); // 1000 / (1 + 0 + 0 + 0) = 1000
Assertions.assertTrue(HarshadNumber.isHarshad(1002)); // 1002 / (1 + 0 + 0 + 2) = 334
Assertions.assertTrue(HarshadNumber.isHarshad(999999999)); // 999999999 / (9*9) = 12345679
 }

@Test
voidtestInvalidHarshadNumbers() {
// Numbers that are not Harshad numbers
Assertions.assertFalse(HarshadNumber.isHarshad(11)); // 11 / (1 + 1) = 5.5
Assertions.assertFalse(HarshadNumber.isHarshad(13)); // 13 / (1 + 3) = 3.25
Assertions.assertFalse(HarshadNumber.isHarshad(17)); // 17 / (1 + 7) = 2.125
Assertions.assertFalse(HarshadNumber.isHarshad(19)); // 19 / (1 + 9) = 1.9
Assertions.assertFalse(HarshadNumber.isHarshad(23)); // 23 / (2 + 3) = 4.6
Assertions.assertFalse(HarshadNumber.isHarshad(101)); // 101 / (1 + 0 + 1) = 50.5
 }

@Test
voidtestZeroThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(0));
 }

@Test
voidtestNegativeNumbersThrowException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(-1));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(-18));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(-100));
 }

@Test
voidtestValidHarshadNumbersWithString() {
// Single digit Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad("1"));
Assertions.assertTrue(HarshadNumber.isHarshad("2"));
Assertions.assertTrue(HarshadNumber.isHarshad("9"));

// Two digit Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad("10"));
Assertions.assertTrue(HarshadNumber.isHarshad("12"));
Assertions.assertTrue(HarshadNumber.isHarshad("18"));

// Large Harshad numbers
Assertions.assertTrue(HarshadNumber.isHarshad("1000"));
Assertions.assertTrue(HarshadNumber.isHarshad("999999999"));
Assertions.assertTrue(HarshadNumber.isHarshad("99999999999100"));
 }

@Test
voidtestInvalidHarshadNumbersWithString() {
// Numbers that are not Harshad numbers
Assertions.assertFalse(HarshadNumber.isHarshad("11"));
Assertions.assertFalse(HarshadNumber.isHarshad("13"));
Assertions.assertFalse(HarshadNumber.isHarshad("19"));
Assertions.assertFalse(HarshadNumber.isHarshad("23"));
 }

@Test
voidtestStringWithZeroThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("0"));
 }

@Test
voidtestStringWithNegativeNumbersThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("-1"));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("-18"));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("-100"));
 }

@Test
voidtestNullStringThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(null));
 }

@Test
voidtestEmptyStringThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(""));
 }

@Test
voidtestInvalidStringThrowsException() {
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("abc"));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("12.5"));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad("12a"));
Assertions.assertThrows(IllegalArgumentException.class, () -> HarshadNumber.isHarshad(" 12 "));
 }

@Test
voidtestMaxLongValue() {
// Test with a large number close to Long.MAX_VALUE
longlargeHarshadCandidate = 9223372036854775800L;
// This specific number may or may not be Harshad, just testing it doesn't crash
try {
HarshadNumber.isHarshad(largeHarshadCandidate);
 } catch (Exceptione) {
Assertions.fail("Should not throw exception for valid large numbers");
 }
 }
}