diff --git a/.github/workflows/golang_test.yml b/.github/workflows/golang_test.yml
index 27979ea..70b1564 100644
--- a/.github/workflows/golang_test.yml
+++ b/.github/workflows/golang_test.yml
@@ -22,7 +22,5 @@ jobs:
           version: v1.51.0
           args: --disable-all -E gofmt --print-linter-name
           skip-build-cache: true
-      - name: run math unit testing
-        run: go test ./math/...
-      - name: run math implementation unit testing
-        run: go test ./math_implementation/...
+      - name: run unit testing
+        run: go test $(go list ./... | grep -v 'basic\|intermediate\|utilities')
diff --git a/math_implementation/armstrong/is_armstrong_test.go b/math_implementation/armstrong/is_armstrong_test.go
index 2e85d35..5c9fc55 100644
--- a/math_implementation/armstrong/is_armstrong_test.go
+++ b/math_implementation/armstrong/is_armstrong_test.go
@@ -34,7 +34,7 @@ var testCase = []struct {
 	},
 }
 
-func testingArmstrong(t *testing.T) {
+func TestArmstrong(t *testing.T) {
 	for _, test := range testCase {
 		t.Run(test.name, func(t *testing.T) {
 			funcResult := cekArmstrong(test.input)
diff --git a/math_implementation/faktorial/faktorial.go b/math_implementation/faktorial/faktorial.go
new file mode 100644
index 0000000..ca1c297
--- /dev/null
+++ b/math_implementation/faktorial/faktorial.go
@@ -0,0 +1,66 @@
+package faktorial
+
+import "errors"
+
+var ArgumentNegatif = errors.New("argumen input harus berupa bilangan bulat non-negatif")
+
+// fungsi untuk menghitung faktorial secara bruteforce
+func Iterasi(n int) (int, error) {
+	if n < 0 {
+		return 0, ArgumentNegatif
+	}
+
+	hasil := 1
+	for i := 2; i <= n; i++ {
+		hasil *= i
+	}
+	return hasil, nil
+}
+
+// fungsi menghitung faktorial secara rekursif
+func Rekursif(n int) (int, error) {
+	if n < 0 {
+		return 0, ArgumentNegatif
+	}
+
+	if n <= 1 {
+		return 1, nil
+	}
+
+	prev, _ := Rekursif(n - 1)
+	return n * prev, nil
+}
+
+// menghitung faktorial menggunakan tree biner (divide and conquer)
+func TreeBin(n int) (int, error) {
+	if n < 0 {
+		return 0, ArgumentNegatif
+	}
+
+	if n == 0 {
+		return 1, nil
+	}
+
+	if n == 1 || n == 2 {
+		return n, nil
+	}
+
+	return produkTree(2, n), nil
+}
+
+func produkTree(l int, r int) int {
+	if l > r {
+		return 1
+	}
+
+	if l == r {
+		return l
+	}
+
+	if r-l == 1 {
+		return l * r
+	}
+
+	m := (l + r) / 2
+	return produkTree(l, m) * produkTree(m+1, r)
+}
diff --git a/math_implementation/faktorial/faktorial_test.go b/math_implementation/faktorial/faktorial_test.go
new file mode 100644
index 0000000..974695c
--- /dev/null
+++ b/math_implementation/faktorial/faktorial_test.go
@@ -0,0 +1,47 @@
+package faktorial
+
+import (
+	"fmt"
+	"testing"
+)
+
+type fungsiFaktorial func(int) (int, error)
+
+var implementasi = map[string]fungsiFaktorial{
+	"Iterasi":  Iterasi,
+	"Rekursif": Rekursif,
+	"Tree":     TreeBin,
+}
+
+var testCase = []struct {
+	n         int
+	ekspetasi int
+}{
+	{0, 1},
+	{1, 1},
+	{6, 720},
+	{9, 362880},
+}
+
+func TestFaktorial(t *testing.T) {
+	for implName, implFunction := range implementasi {
+		t.Run(implName+" error input negatif", func(t *testing.T) {
+			_, error := implFunction(-1)
+			if error != ArgumentNegatif {
+				t.Errorf("tidak ada error dari input negatif")
+			}
+		})
+
+		for _, tc := range testCase {
+			t.Run(fmt.Sprintf("%s dengan input %d", implName, tc.n), func(t *testing.T) {
+				aktual, err := implFunction(tc.n)
+				if err != nil {
+					t.Errorf("add error")
+				}
+				if aktual != tc.ekspetasi {
+					t.Errorf("ekspetasi: %d, aktual: %d", tc.ekspetasi, aktual)
+				}
+			})
+		}
+	}
+}