diff --git a/array-smallest-missing-number/array-smallest-missing-number_test.go b/array-smallest-missing-number/array-smallest-missing-number_test.go
new file mode 100644
index 0000000..2a717d2
--- /dev/null
+++ b/array-smallest-missing-number/array-smallest-missing-number_test.go
@@ -0,0 +1,36 @@
+// ====================================================
+// Data-Structures-with-Go Copyright(C) 2017 Furkan Türkal
+// This program comes with ABSOLUTELY NO WARRANTY; This is free software,
+// and you are welcome to redistribute it under certain conditions; See
+// file LICENSE, which is part of this source code package, for details.
+// ====================================================
+
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestFindFirstMissing(t *testing.T) {
+	var testDatas = []struct {
+		ArrayIn []int
+		Start   int
+		End     int
+		Out     int
+	}{
+		{[]int{0, 1, 2, 4, 5}, 0, 4, 3},
+		{[]int{0, 1, 2, 3, 4, 6, 8, 9, 10}, 0, 5, 5},
+		{[]int{0, 1, 2, 3, 4, 6, 8, 9, 10}, 0, 8, 5},
+		{[]int{0, 1, 2, 3, 4, 5, 6, 8, 9, 10}, 0, 8, 7},
+		{[]int{1, 2, 3, 4, 5}, 0, 5, 0},
+	}
+	for _, data := range testDatas {
+		expected := data.Out
+		actual := findFirstMissing(data.ArrayIn, data.Start, data.End)
+
+		if !reflect.DeepEqual(expected, actual) {
+			t.Errorf("FindFirstMissing: Expected: %d, Actual: %d", expected, actual)
+		}
+	}
+}