Remove main function, improve docstring, add JUnit tests for KrishnamurthyNumber. (#5881)

src/test/java/com/thealgorithms/maths/KrishnamurthyNumberTest.java

@@ -0,0 +1,62 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the KrishnamurthyNumber class.
+ */
+public class KrishnamurthyNumberTest {
+
+    /**
+     * Test the isKrishnamurthy method with a known Krishnamurthy number.
+     */
+    @Test
+    public void testIsKrishnamurthyTrue() {
+        assertTrue(KrishnamurthyNumber.isKrishnamurthy(145));
+    }
+
+    /**
+     * Test the isKrishnamurthy method with a number that is not a Krishnamurthy number.
+     */
+    @Test
+    public void testIsKrishnamurthyFalse() {
+        assertFalse(KrishnamurthyNumber.isKrishnamurthy(123));
+    }
+
+    /**
+     * Test the isKrishnamurthy method with zero.
+     */
+    @Test
+    public void testIsKrishnamurthyZero() {
+        assertFalse(KrishnamurthyNumber.isKrishnamurthy(0));
+    }
+
+    /**
+     * Test the isKrishnamurthy method with a negative number.
+     */
+    @Test
+    public void testIsKrishnamurthyNegative() {
+        assertFalse(KrishnamurthyNumber.isKrishnamurthy(-145));
+    }
+
+    /**
+     * Test the isKrishnamurthy method with a single-digit Krishnamurthy number.
+     */
+    @Test
+    public void testIsKrishnamurthySingleDigitTrue() {
+        assertTrue(KrishnamurthyNumber.isKrishnamurthy(1));
+        assertTrue(KrishnamurthyNumber.isKrishnamurthy(2));
+    }
+
+    /**
+     * Test the isKrishnamurthy method with a single-digit number that is not a Krishnamurthy number.
+     */
+    @Test
+    public void testIsKrishnamurthySingleDigitFalse() {
+        assertFalse(KrishnamurthyNumber.isKrishnamurthy(3));
+        assertFalse(KrishnamurthyNumber.isKrishnamurthy(4));
+    }
+}