diff --git a/bin/StringCalculator.class b/bin/StringCalculator.class
index a937b0c..9a09888 100644
Binary files a/bin/StringCalculator.class and b/bin/StringCalculator.class differ
diff --git a/bin/StringCalculatorTest.class b/bin/StringCalculatorTest.class
index d44b83f..e9eabbc 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..9d59a7b 100644
--- a/src/StringCalculator.java
+++ b/src/StringCalculator.java
@@ -1,9 +1,59 @@
+import java.util.Scanner;
+import java.util.stream.IntStream;
 
 public class StringCalculator {
-	public int add(String numbersStr) {
-		// Returns the sum of the numbers given in numbersStr
-		
-		// not yet implemented
-		return 0;
+	
+	public int add(String numbersStr) throws StringCalculatorException {
+		String[] strArray = toStringArray(numbersStr);
+		int[] intArray = toIntArray(strArray);
+		int sum = IntStream.of(intArray).sum();
+		return sum;
 	}
-}
+	
+	public String[] toStringArray (String numbersStr) throws StringCalculatorException {
+		String text1 = handleUnknownNumbers(numbersStr);
+		String text2 = handleEmptyString(text1);
+		String text3 = handleLineBreakAndComma(text2);
+		String text4 = handleAlphabeticAndNegative(text3);
+		String[] split = text4.split(",");
+		return split;
+	}
+	
+	public int[] toIntArray (String[] arr) {
+		int[] ints = new int [arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			ints[i] = Integer.parseInt(arr[i]);
+		}
+		return ints;
+	}
+	
+	public String handleLineBreakAndComma (String numbersStr) throws StringCalculatorException{
+		if (numbersStr.contains(",\n")) {
+			throw new StringCalculatorException();
+		}else{
+		String text = numbersStr.replace("\n", ",");
+		return text;
+		}
+	}	
+	public String handleEmptyString (String numbersStr) {
+		if (numbersStr == "0") {
+			return "";
+		}else { 
+			return numbersStr;
+		}
+	}
+	public String handleUnknownNumbers(String numbersStr) throws StringCalculatorException  {
+		if (numbersStr.length() > 3 && numbersStr.contains("\n") == false) {
+			throw new StringCalculatorException();
+		}else {
+			return numbersStr;
+		}
+	}
+	public String handleAlphabeticAndNegative(String numbersStr) throws StringCalculatorException {
+		if (numbersStr.matches("[0-9,]+") == false) {
+			throw new StringCalculatorException();
+		}else {
+			return numbersStr;
+		}
+	}
+}
\ No newline at end of file
diff --git a/src/StringCalculatorException.java b/src/StringCalculatorException.java
index da71147..0856125 100644
--- a/src/StringCalculatorException.java
+++ b/src/StringCalculatorException.java
@@ -1,4 +1,4 @@
 
 public class StringCalculatorException extends Exception {
-
+	
 }
diff --git a/tests/StringCalculatorTest.java b/tests/StringCalculatorTest.java
index 4ec9afe..619b07b 100644
--- a/tests/StringCalculatorTest.java
+++ b/tests/StringCalculatorTest.java
@@ -5,8 +5,158 @@
 public class StringCalculatorTest {
 
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void testOneNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String[] result = {"1"};
+		int[] intArray = calculator.toIntArray(result);
+		int[] ints2 = {1};
+		//Assert
+		assertArrayEquals(intArray, ints2);
+	}
+	
+	@Test
+	public void testTwoIntNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String[] result = {"1","2"};
+		int[] intArray = calculator.toIntArray(result);
+		int[] ints2 = {1,2};
+		//Assert
+		assertArrayEquals(intArray, ints2);
+	}
+	
+	@Test
+	public void testTwoStringNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1,2";
+		String[] stringArray = calculator.toStringArray(result);
+		String[] stringArray2 = {"1", "2"};
+		//Assert
+		assertArrayEquals(stringArray, stringArray2);
+	}
+	
+	@Test
+	public void testThreeStringNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1\n2,3";
+		String[] stringArray = calculator.toStringArray(result);
+		String[] stringArray2 = {"1","2","3"};
+		//Assert
+		assertArrayEquals(stringArray, stringArray2);
+	}
+	
+	@Test
+	public void testLineBreak() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1\n2,3";
+		String string = calculator.handleLineBreakAndComma(result);
+		String string2 = "1,2,3";
+		//Assert
+		assertEquals(string, string2);
+	}
+	
+	@Test (expected = StringCalculatorException.class)
+	public void testComma() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1,\n2,3";
+		// This statement should cause an exception
+		calculator.handleLineBreakAndComma(result);
+	}
+	@Test
+	public void testEmptyString() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "0";
+		String string = calculator.handleEmptyString(result);
+		String string2 = "";
+		//Assert
+		assertEquals(string, string2);
+		System.out.println(string);
+	}
+	
+	@Test (expected = StringCalculatorException.class)
+	public void testUnknowNumbers() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1,2,3";
+		// This statement should cause an exception
+		calculator.handleUnknownNumbers(result);
+	}
+	@Test (expected = StringCalculatorException.class)
+	public void testAlphapeticAndNegative() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "A";
+		// This statement should cause an exception
+		calculator.handleAlphabeticAndNegative(result);
+	}
+	@Test (expected = StringCalculatorException.class)
+	public void testAlphapeticAndNegative2() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "-2";
+		// This statement should cause an exception
+		calculator.handleAlphabeticAndNegative(result);
+		System.out.println(result);
+	}
+	
+	@Test
+	public void testAddLineBreak() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1\n2,3";
+		int toInt = calculator.add(result);
+		int sum = 6;
+		//Assert
+		assertEquals(toInt, sum);
+	}
+	@Test
+	public void testAddTwoNumbers() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "1,2";
+		int toInt = calculator.add(result);
+		int sum = 3;
+		//Assert
+		assertEquals(toInt, sum);
+	}
+	@Test
+	public void testAddZeroAndNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "0,2";
+		int toInt = calculator.add(result);
+		int sum = 2;
+		//Assert
+		assertEquals(toInt, sum);
+	}
+	@Test
+	public void testAddOneNumber() throws StringCalculatorException {
+		//Arrange
+		StringCalculator calculator = new StringCalculator();
+		//Act
+		String result = "2";
+		int toInt = calculator.add(result);
+		int sum = 2;
+		//Assert
+		assertEquals(toInt, sum);
 	}
-
 }