diff --git a/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/happynumber/HappyNumberUnitTest.java b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/happynumber/HappyNumberUnitTest.java
new file mode 100644
index 0000000000..5cdf1a82c5
--- /dev/null
+++ b/algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/happynumber/HappyNumberUnitTest.java
@@ -0,0 +1,82 @@
+package com.baeldung.algorithms.happynumber;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.jupiter.api.Test;
+
+class HappyNumberDecider {
+
+    public static boolean isHappyNumber(int n) {
+        Set<Integer> checkedNumbers = new HashSet<>();
+        while (true) {
+            n = sumDigitsSquare(n);
+            if (n == 1) {
+                return true;
+            }
+            if (checkedNumbers.contains(n)) {
+                return false;
+            }
+            checkedNumbers.add(n);
+        }
+    }
+
+    public static boolean isHappyNumber2(int n) {
+        int slow = n;
+        int fast = n;
+        do {
+            slow = sumDigitsSquare(slow);
+            fast = sumDigitsSquare(sumDigitsSquare(fast));
+        } while (slow != fast);
+
+        return slow == 1;
+    }
+
+    private static int sumDigitsSquare(int n) {
+        int squareSum = 0;
+        while (n != 0) {
+            squareSum += (n % 10) * (n % 10);
+            n /= 10;
+        }
+        return squareSum;
+    }
+}
+
+public class HappyNumberUnitTest {
+
+    @Test
+    void whenUsingIsHappyNumber_thenGetTheExpectedResult() {
+        assertTrue(HappyNumberDecider.isHappyNumber(7));
+        assertTrue(HappyNumberDecider.isHappyNumber(10));
+        assertTrue(HappyNumberDecider.isHappyNumber(13));
+        assertTrue(HappyNumberDecider.isHappyNumber(19));
+        assertTrue(HappyNumberDecider.isHappyNumber(23));
+
+        assertFalse(HappyNumberDecider.isHappyNumber(4));
+        assertFalse(HappyNumberDecider.isHappyNumber(6));
+        assertFalse(HappyNumberDecider.isHappyNumber(11));
+        assertFalse(HappyNumberDecider.isHappyNumber(15));
+        assertFalse(HappyNumberDecider.isHappyNumber(20));
+
+    }
+
+    @Test
+    void whenUsingIsHappyNumber2_thenGetTheExpectedResult() {
+        assertTrue(HappyNumberDecider.isHappyNumber2(7));
+        assertTrue(HappyNumberDecider.isHappyNumber2(10));
+        assertTrue(HappyNumberDecider.isHappyNumber2(13));
+        assertTrue(HappyNumberDecider.isHappyNumber2(19));
+        assertTrue(HappyNumberDecider.isHappyNumber2(23));
+
+        assertFalse(HappyNumberDecider.isHappyNumber2(4));
+        assertFalse(HappyNumberDecider.isHappyNumber2(6));
+        assertFalse(HappyNumberDecider.isHappyNumber2(11));
+        assertFalse(HappyNumberDecider.isHappyNumber2(15));
+        assertFalse(HappyNumberDecider.isHappyNumber2(20));
+
+    }
+
+}
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