Add test for PlusOperator in OperatorExecutorTest

Author: parkcheayeon

feature/stoplist/src/main/java/com/chaeny/busoda/stoplist/operator/OperatorExecutor.java

@@ -4,7 +4,7 @@
 import java.util.List;
 
 public class OperatorExecutor {
-    public int main(String[] args) {
+    public int executeOperation(String[] args) {
         if (args.length < 3) {
             throw new IllegalArgumentException("모두 입력해주세요.");
         }

feature/stoplist/src/test/java/com/chaeny/busoda/stoplist/operator/OperatorExecutorTest.java

@@ -0,0 +1,16 @@
+package com.chaeny.busoda.stoplist.operator;
+
+import static org.junit.Assert.*;
+import org.junit.Test;
+
+public class OperatorExecutorTest {
+
+    OperatorExecutor operatorExecutor = new OperatorExecutor();
+
+    @Test
+    public void testPlusOperator() {
+        String[] args = {"2", "+", "2"};
+        int result = operatorExecutor.executeOperation(args);
+        assertEquals(result, 4);
+    }
+}