diff --git a/arrays/sum.go b/arrays/sum.go
new file mode 100644
index 0000000..78c8998
--- /dev/null
+++ b/arrays/sum.go
@@ -0,0 +1,9 @@
+package main
+
+func Sum(numbers []int) int {
+	sum := 0
+	for _, n := range numbers {
+		sum += n
+	}
+	return sum
+}
diff --git a/arrays/sum_test.go b/arrays/sum_test.go
new file mode 100644
index 0000000..f94c4ff
--- /dev/null
+++ b/arrays/sum_test.go
@@ -0,0 +1,29 @@
+package main
+
+import "testing"
+
+func TestSum(t *testing.T) {
+
+	t.Run("collection of 5 numbers", func(t *testing.T) {
+		numbers := []int{1, 2, 3, 4, 5}
+
+		got := Sum(numbers)
+		want := 15
+
+		if got != want {
+			t.Errorf("got %d want %d given, %v", got, want, numbers)
+		}
+	})
+
+	t.Run("collection of any size", func(t *testing.T) {
+		numbers := []int{1, 2, 3}
+
+		got := Sum(numbers)
+		want := 6
+
+		if got != want {
+			t.Errorf("got %d want %d given, %v", got, want, numbers)
+		}
+	})
+
+}