diff --git a/src/class01/Code04_BSExist.java b/src/class01/Code04_BSExist.java
index 9010182..49bc7f2 100644
--- a/src/class01/Code04_BSExist.java
+++ b/src/class01/Code04_BSExist.java
@@ -1,5 +1,7 @@
 package class01;
 
+import java.util.Arrays;
+
 public class Code04_BSExist {
 
 	public static boolean exist(int[] sortedArr, int num) {
@@ -26,5 +28,42 @@ public class Code04_BSExist {
 		}
 		return sortedArr[L] == num;
 	}
+	
+	// for test
+	public static boolean test(int[] sortedArr, int num) {
+		for(int cur : sortedArr) {
+			if(cur == num) {
+				return true;
+			}
+		}
+		return false;
+	}
+	
+	
+	// for test
+	public static int[] generateRandomArray(int maxSize, int maxValue) {
+		int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
+		for (int i = 0; i < arr.length; i++) {
+			arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+		}
+		return arr;
+	}
+	
+	public static void main(String[] args) {
+		int testTime = 500000;
+		int maxSize = 10;
+		int maxValue = 100;
+		boolean succeed = true;
+		for (int i = 0; i < testTime; i++) {
+			int[] arr = generateRandomArray(maxSize, maxValue);
+			Arrays.sort(arr);
+			int value = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
+			if (test(arr, value) != exist(arr, value)) {
+				succeed = false;
+				break;
+			}
+		}
+		System.out.println(succeed ? "Nice!" : "Fucking fucked!");
+	}
 
 }