Add array sum module

arrays/sum.go

@@ -0,0 +1,10 @@
+package main
+
+func Sum(numbers []int) int {
+	sum := 0
+	// example: for ... in equivalent, first var has index
+	for _, number := range numbers {
+		sum += number
+	}
+	return sum
+}

arrays/sum_test.go

@@ -0,0 +1,27 @@
+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)
+		}
+	})
+}