Ukonczony krok pierwszy

StringCalculator/.idea/vcs.xml

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$/.." vcs="Git" />
     <mapping directory="$PROJECT_DIR$" vcs="Git" />
   </component>
 </project>

StringCalculator/src/main/java/pl/dmcs/Calculator.java

@@ -1,4 +1,15 @@
 package pl.dmcs;
 
 public class Calculator {
+    public int add(String numbers) {
+        if (numbers == null || numbers.isEmpty()) {
+            return 0;
+        }
+        String[] numArray = numbers.split(",");
+        int sum = 0;
+        for (String num : numArray) {
+            sum += Integer.parseInt(num);
+        }
+        return sum;
+    }
 }

StringCalculator/src/test/java/pl/dmcs/CalculatorTest.java

@@ -1,4 +1,25 @@
 package pl.dmcs;
 
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 public class CalculatorTest {
+
+    private final Calculator calculator = new Calculator();
+
+    @Test
+    public void testAddEmptyString() {
+        assertEquals(0, calculator.add(""));
+    }
+
+    @Test
+    public void testAddOneNumber() {
+        assertEquals(1, calculator.add("1"));
+    }
+
+    @Test
+    public void testAddTwoNumbers() {
+        assertEquals(3, calculator.add("1,2"));
+    }
+
 }