diff --git a/internal/internal.go b/internal/internal.go
index 0b04b79..1a804b6 100644
--- a/internal/internal.go
+++ b/internal/internal.go
@@ -3,3 +3,7 @@ package internal
 func Add(a, b int) int {
 	return a + b
 }
+
+func Sub(a, b int) int {
+	return a - b
+}
diff --git a/internal/internal_test.go b/internal/internal_test.go
index 8bdc2a8..16d576e 100644
--- a/internal/internal_test.go
+++ b/internal/internal_test.go
@@ -28,3 +28,24 @@ func TestAdd(t *testing.T) {
 		})
 	}
 }
+func TestSub(t *testing.T) {
+	var tc = []struct {
+		A        int
+		B        int
+		Expected int
+	}{
+		{A: 1, B: 0, Expected: 1},
+		{A: 1, B: 1, Expected: 0},
+		{A: 0, B: -5, Expected: -5},
+	}
+
+	for _, test := range tc {
+		name := fmt.Sprintf("%d-%d", test.A, test.B)
+		t.Run(name, func(t *testing.T) {
+			result := internal.Sub(test.A, test.B)
+			if result != test.Expected {
+				t.Errorf("Got %d, expected %d", result, test.Expected)
+			}
+		})
+	}
+}