step1

build.gradle

@@ -1,5 +1,6 @@
 plugins {
     id 'java'
+    id 'org.jetbrains.kotlin.jvm' version '1.7.21'
 }
 
 version '1.0-SNAPSHOT'
@@ -11,6 +12,7 @@ repositories {
 dependencies {
     testImplementation 'org.assertj:assertj-core:3.22.0'
     testImplementation 'org.junit.jupiter:junit-jupiter:5.8.2'
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
 }
 
 java {

src/main/java/util/StringCalculator.java

@@ -0,0 +1,49 @@
+package util;
+
+public class StringCalculator {
+
+    public int calculate(String input) {
+        validateInput(input);
+        String[] tokens = input.split(" ");
+
+        int result = Integer.parseInt(tokens[0]);
+
+        for (int i = 1; i < tokens.length; i += 2) {
+            String operator = tokens[i];
+            int nextNumber = Integer.parseInt(tokens[i+1]);
+            result = operate(operator, result, nextNumber);
+        }
+        return result;
+    }
+
+    private void validateInput(String input) {
+        if (input == null || input.isBlank()) {
+            throw new IllegalArgumentException("input이 null이거나 빈 문자열입니다.");
+        }
+    }
+
+    private int operate(String operator, int left, int right) {
+        switch (operator) {
+            case "+":
+                return left + right;
+            case "-":
+                return left - right;
+            case "*":
+                return left * right;
+            case "/":
+                return division(left, right);
+            default:
+                throw new IllegalArgumentException("올바른 사칙연산 부호가 아닙니다");
+        }
+    }
+
+    int division(int left, int right) {
+        if (right == 0) {
+            throw new IllegalArgumentException("0으로 나눌 수 없습니다.");
+        }
+        if (left % right != 0) {
+            throw new IllegalArgumentException("나눔 값이 정수가 아닙니다.");
+        }
+        return left / right;
+    }
+}

src/test/java/util/StringCalculatorTest.java

@@ -0,0 +1,56 @@
+package util;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.assertj.core.api.Assertions.*;
+
+public class StringCalculatorTest {
+    private StringCalculator stringCalculator;
+
+    @BeforeEach
+    void setUp() {
+        stringCalculator = new StringCalculator();
+    }
+
+    @Test
+    void testAdd() {
+        String input = "2 + 3";
+        int expected = 5;
+        int result = stringCalculator.calculate(input);
+        assertThat(result).isEqualTo(expected);
+    }
+
+    @Test
+    void testSubtract() {
+        String input = "2 - 3";
+        int expected = -1;
+        int result = stringCalculator.calculate(input);
+        assertThat(result).isEqualTo(expected);
+    }
+
+    @Test
+    void testMultiply() {
+        String input = "2 * 3";
+        int expected = 6;
+        int result = stringCalculator.calculate(input);
+        assertThat(result).isEqualTo(expected);
+    }
+
+    @Test
+    void testDivide() {
+        String input = "20 / 2";
+        int expected = 10;
+        int result = stringCalculator.calculate(input);
+        assertThat(result).isEqualTo(expected);
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"", " "})
+    void intputNullOrEmpty(String input) {
+        assertThatIllegalArgumentException()
+                .isThrownBy(() -> stringCalculator.calculate(input));
+    }
+}