diff --git a/problems/happy-number/happy_number.go b/problems/happy-number/happy_number.go
index 2bce4663d..4b470ebe6 100644
--- a/problems/happy-number/happy_number.go
+++ b/problems/happy-number/happy_number.go
@@ -1 +1,16 @@
 package happy_number
+
+func isHappy(n int) bool {
+	m := make(map[int]bool)
+	for n != 1 && !m[n] {
+		m[n] = true
+		sum := 0
+		for n > 0 {
+			x := n % 10
+			sum += x * x
+			n /= 10
+		}
+		n = sum
+	}
+	return n == 1
+}
diff --git a/problems/happy-number/happy_number_test.go b/problems/happy-number/happy_number_test.go
index 2bce4663d..1baca9617 100644
--- a/problems/happy-number/happy_number_test.go
+++ b/problems/happy-number/happy_number_test.go
@@ -1 +1,31 @@
 package happy_number
+
+import "testing"
+
+type caseType struct {
+	input    int
+	expected bool
+}
+
+func TestIsHappy(t *testing.T) {
+	tests := [...]caseType{
+		{
+			input:    19,
+			expected: true,
+		},
+		{
+			input:    1,
+			expected: true,
+		},
+		{
+			input:    0,
+			expected: false,
+		},
+	}
+	for _, tc := range tests {
+		output := isHappy(tc.input)
+		if output != tc.expected {
+			t.Fatalf("input: %v, output: %v, expected: %v", tc.input, output, tc.expected)
+		}
+	}
+}