the first one

calculator/calculator.go

@@ -0,0 +1,5 @@
+// Package calculator does simple calculations.
+package calculator // Add takes two numbers and returns the result of adding them together.
+func Add(a, b float64) float64 {
+        return a + b
+}

calculator/calculator_test.go

@@ -0,0 +1,16 @@
+package calculator_test
+
+import (
+        "calculator"
+        "testing"
+)
+
+func TestAdd(t *testing.T) {
+        t.Parallel()
+        var want float64 = 4
+        got := calculator.Add(2, 2)
+        if want != got {
+                t.Errorf("want %f, got %f", want, got)
+        }
+}
+

calculator/go.mod

@@ -0,0 +1,4 @@
+module calculator
+
+go 1.22.4
+