integers: add adder

integers/adder.go

@@ -0,0 +1,5 @@
+package integers
+
+func Add(x, y int) int {
+	return x + y
+}

integers/adder_test.go

@@ -0,0 +1,12 @@
+package integers
+
+import "testing"
+
+func TestAdder(t *testing.T) {
+	sum := Add(2, 2)
+	expected := 4
+
+	if sum != expected {
+		t.Errorf("got %d, expected %d", sum, expected)
+	}
+}