diff --git a/bin/StringCalculator.class b/bin/StringCalculator.class
index a937b0c..c7cfac7 100644
Binary files a/bin/StringCalculator.class and b/bin/StringCalculator.class differ
diff --git a/bin/StringCalculatorException.class b/bin/StringCalculatorException.class
index 4bd9894..3fd5967 100644
Binary files a/bin/StringCalculatorException.class and b/bin/StringCalculatorException.class differ
diff --git a/bin/StringCalculatorTest.class b/bin/StringCalculatorTest.class
index d44b83f..16a2161 100644
Binary files a/bin/StringCalculatorTest.class and b/bin/StringCalculatorTest.class differ
diff --git a/src/StringCalculator.java b/src/StringCalculator.java
index 487916b..902396c 100644
--- a/src/StringCalculator.java
+++ b/src/StringCalculator.java
@@ -1,9 +1,61 @@
 
 public class StringCalculator {
-	public int add(String numbersStr) {
+	public int add(String numbersStr) throws StringCalculatorException {
 		// Returns the sum of the numbers given in numbersStr
+		int sum = 0;
+		int[] newNumbersInt = invalidNegtive(numbersStr);
 		
-		// not yet implemented
-		return 0;
+		if(newNumbersInt.length == 0){
+			return 0;
+		}
+				
+		for(int i=0; i<newNumbersInt.length; i++){
+			sum = sum + newNumbersInt[i];
+			}
+				
+		return sum;
+	
+	}
+	
+	public String handleNewLines(String numberStr){
+		String newString = numberStr.replaceAll("\n", ",");
+		return newString;
+	}
+	
+	public int counterSpliter(String newString){
+		int count = 0;
+		
+		for(int i=0;i<newString.length(); i++){
+			if(newString.charAt(i) == ','){
+				count++;
+			}
+		}
+		return count;
+	}
+	
+	public int[] invalidNegtive(String numbersStr) throws StringCalculatorException{
+		String numberStr = handleNewLines(numbersStr);
+		int count1 = counterSpliter(numberStr);
+		String[] newString = numberStr.split(",");
+		int[] numbersInt = new int[newString.length];
+		
+		try{
+			for(int i=0; i< numbersInt.length; i++){
+				int integer = Integer.parseInt(newString[i]);
+				
+				if(integer<0){
+					throw new StringCalculatorException("Negtive number!");
+				} 
+				
+				if(count1 != (numbersInt.length - 1)){
+					throw new StringCalculatorException("invalid!");
+				}
+				numbersInt[i] = integer; 
+			}			
+			}catch(NumberFormatException e){
+				throw new StringCalculatorException("invalid!");
+		}
+		
+		return numbersInt;
 	}
 }
diff --git a/src/StringCalculatorException.java b/src/StringCalculatorException.java
index da71147..d8ec247 100644
--- a/src/StringCalculatorException.java
+++ b/src/StringCalculatorException.java
@@ -1,4 +1,7 @@
 
 public class StringCalculatorException extends Exception {
+	public StringCalculatorException(String message){
+		super(message);
+	}
 
 }
diff --git a/tests/StringCalculatorTest.java b/tests/StringCalculatorTest.java
index 4ec9afe..580d7a4 100644
--- a/tests/StringCalculatorTest.java
+++ b/tests/StringCalculatorTest.java
@@ -5,8 +5,101 @@
 public class StringCalculatorTest {
 
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void testReturn_Sum_1_2() throws StringCalculatorException {
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int sum = cal.add("1,2");
+		assertEquals(3, sum);
+		
+	}
+	
+	@Test
+	public void testReturn_Sum_0() throws StringCalculatorException {
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int sum = cal.add("0");
+		assertEquals(0, sum);		
+	}
+	
+	@Test
+	public void testReturn_Sum_1_2_3() throws StringCalculatorException {
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int sum = cal.add("1,2,3");
+		assertEquals(6, sum);
+		
+	}
+	
+	@Test
+	public void testHandle_NewLine_1_2() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		String str = cal.handleNewLines("1\n2");
+		assertEquals("1,2", str);
+	}
+	
+	@Test
+	public void testHandle_NewLine_1_2_3() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		String str = cal.handleNewLines("1,2\n3");
+		assertEquals("1,2,3", str);
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_Invalid1() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] numbers = cal.invalidNegtive("1,2\n");
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_Negtive() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] numbers = cal.invalidNegtive("-1");	
+	}
+	
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_Invalid() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] numbers = cal.invalidNegtive("abc");
+	}
+	
+
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_1_2_a() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] sum = cal.invalidNegtive("1,2,a");
+	}
+	
+
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_1_2_valid() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] sum = cal.invalidNegtive("1,2,#");
+	}
+	
+
+	@Test(expected = StringCalculatorException.class)
+	public void testInvalidNegtive_1_invalid() throws StringCalculatorException{
+		//Arrange
+		StringCalculator cal = new StringCalculator();
+		//Act
+		int[] sum = cal.invalidNegtive("1,\n");
 	}
 
 }