diff --git a/src/RomanNumerals.java b/src/RomanNumerals.java
index 20904f0..54888f7 100644
--- a/src/RomanNumerals.java
+++ b/src/RomanNumerals.java
@@ -1,8 +1,113 @@
+import java.util.ArrayList;
 
 public class RomanNumerals {
-	public int convertToInteger(String romanNum) {
-		// To be Implemented
-		return 0;
+	
+	public int convertToInteger(String romanNum) throws RomanNumeralsInvalidFormatException {
+		int i, res = 0, temp;
 		
+		if (!invalidFormatCheck(romanNum)) {
+			throw new RomanNumeralsInvalidFormatException();
+		}
+		
+		ArrayList<Integer> splited = splitGroup(romanNum);
+		
+		if (!invalidSubtractCheck(splited)) {
+			throw new RomanNumeralsInvalidFormatException();
+		}
+		
+		return calculateResult(splited);
+	}
+	
+	private int calculateResult(ArrayList<Integer> splited) {
+		int i, res=0, temp;
+		int lastindex = splited.size() - 1;
+		int lastvalue = splited.get(lastindex);
+		for (i=lastindex;i>=0;i--) {
+			temp = splited.get(i);
+			if (temp >= lastvalue) {
+				res += temp;
+			}
+			else {
+				res -= temp;
+			}
+			lastvalue = temp;
+		}
+		return res;
+	}
+	
+	private ArrayList<Integer> splitGroup(String romanNum) {
+		ArrayList<Integer> result = new ArrayList<Integer>();
+		int i, count=0;
+		int current = getValue(romanNum.charAt(0));
+		for (i=0;i<romanNum.length();i++) {
+			if (current == getValue(romanNum.charAt(i))) {
+				count++;
+			}
+			else {
+				result.add(count*current);
+				count = 1;
+				current = getValue(romanNum.charAt(i));
+			}
+		}
+		result.add(count*current); //last one
+		return result;
+	}
+	
+	private boolean invalidSubtractCheck(ArrayList<Integer> romanList) {
+		int lastindex = romanList.size() - 1;
+		int lastvalue = romanList.get(lastindex);
+		int i, temp;
+		for (i=lastindex-1;i>=0;i--) {
+			temp = romanList.get(i);
+			if ((temp < lastvalue && (!isnotFive(temp))) || (temp*10 < lastvalue)) {
+				//only 1, 10, 100 allowed as subtractor
+				//I can be subtracted from maximum 10, X from 100, ...
+				return false;
+			}
+		}
+		return true;
+	}
+	
+	private boolean invalidFormatCheck(String romanNum) {
+		int lastindex = romanNum.length() - 1;
+		char last = romanNum.charAt(lastindex);
+		int i, count=1;
+		for (i=lastindex-1;i>=0;i--) {
+			if (romanNum.charAt(i)==last) {
+				count += 1;
+				if (!isnotFive(getValue(last)) || count > 3) {
+					return false;
+				}
+			}
+			else if (getValue(romanNum.charAt(i)) == 0) {
+				//default value, invalid character
+				return false;
+			}
+			else {
+				count = 1;
+			}
+			
+		}
+		return true;
+	}
+	
+	private boolean isnotFive(int c) {
+		if (c == 1 || c == 10 || c == 100 || c == 1000) {
+			return true;
+		}
+		return false;
+	}
+	
+	private static int getValue(char a) {
+		switch(a) {
+			case 'I': return 1;
+			case 'V': return 5;
+			case 'X': return 10;
+			case 'L': return 50;
+			case 'C': return 100;
+			case 'D': return 500;
+			case 'M': return 1000;
+			default: return 0;
+		}
 	}
 }
diff --git a/src/RomanNumeralsInvalidFormatException.java b/src/RomanNumeralsInvalidFormatException.java
new file mode 100644
index 0000000..62b0355
--- /dev/null
+++ b/src/RomanNumeralsInvalidFormatException.java
@@ -0,0 +1,4 @@
+
+public class RomanNumeralsInvalidFormatException extends Exception {
+
+}
diff --git a/tests/TestRomanNumerals.java b/tests/TestRomanNumerals.java
index 5d1de75..b4d1eb5 100644
--- a/tests/TestRomanNumerals.java
+++ b/tests/TestRomanNumerals.java
@@ -5,8 +5,373 @@
 public class TestRomanNumerals {
 
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void convertToInteger_I_1() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("I");
+		//Assert
+		assertEquals(1, res);
 	}
+	
+	@Test
+	public void convertToInteger_V_5() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("V");
+		//Assert
+		assertEquals(5, res);
+	}
+	
+	@Test
+	public void convertToInteger_X_10() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("X");
+		//Assert
+		assertEquals(10, res);
+	}
+	
+	@Test
+	public void convertToInteger_L_50() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("L");
+		//Assert
+		assertEquals(50, res);
+	}
+	
+	@Test
+	public void convertToInteger_C_100() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("C");
+		//Assert
+		assertEquals(100, res);
+	}
+	
+	@Test
+	public void convertToInteger_D_500() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("D");
+		//Assert
+		assertEquals(500, res);
+	}
+	
+	@Test
+	public void convertToInteger_M_1000() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("M");
+		//Assert
+		assertEquals(1000, res);
+	}
+	
+	@Test
+	public void convertToInteger_III_3() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("III");
+		//Assert
+		assertEquals(3, res);
+	}
+	
+	@Test
+	public void convertToInteger_XXX_30() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XXX");
+		//Assert
+		assertEquals(30, res);
+	}
+	
+	@Test
+	public void convertToInteger_CCC_300() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("CCC");
+		//Assert
+		assertEquals(300, res);
+	}
+	
+	@Test
+	public void convertToInteger_MMM_3000() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("MMM");
+		//Assert
+		assertEquals(3000, res);
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_VV_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("VV");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_LL_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("LL");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_DD_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("DD");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_IIII_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IIII");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_XXXX_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XXXX");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_CCCC_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("CCCC");
+
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_MMMM_notvalid() throws RomanNumeralsInvalidFormatException{
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("MMMM");
 
+	}
+	
+	@Test
+	public void convertToInteger_IV_4() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IV");
+		//Assert
+		assertEquals(4, res);
+	}
+	
+	@Test
+	public void convertToInteger_IX_9() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IX");
+		//Assert
+		assertEquals(9, res);
+	}
+	
+	@Test
+	public void convertToInteger_XL_40() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XL");
+		//Assert
+		assertEquals(40, res);
+	}
+	
+	@Test
+	public void convertToInteger_XC_90() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XC");
+		//Assert
+		assertEquals(90, res);
+	}
+	
+	@Test
+	public void convertToInteger_CD_400() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("CD");
+		//Assert
+		assertEquals(400, res);
+	}
+	
+	@Test
+	public void convertToInteger_CM_900() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("CM");
+		//Assert
+		assertEquals(900, res);
+	}
+	
+	@Test
+	public void convertToInteger_XXIV_24() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XXIV");
+		//Assert
+		assertEquals(24, res);
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_VL_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("VL");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_LC_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("LC");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_DM_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("DM");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_IVXMM_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IVXMM");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_XM_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XM");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_XD_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("XD");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_IL_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IL");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_IC_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IC");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_ID_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("ID");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_IM_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("IM");
+		
+	}
+	
+	@Test
+	public void convertToInteger_MCMXCVI_1996() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("MCMXCVI");
+		//Assert
+		assertEquals(1996, res);
+	}
+	
+	@Test
+	public void convertToInteger_MMMDXLIII_3543() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("MMMDXLIII");
+		//Assert
+		assertEquals(3543, res);
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_FF_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("FF");
+		
+	}
+	
+	@Test (expected = RomanNumeralsInvalidFormatException.class)
+	public void convertToInteger_MMMSXLIII_invalid() throws RomanNumeralsInvalidFormatException {
+		//Arrange
+		RomanNumerals converter = new RomanNumerals();
+		//Act
+		int res = converter.convertToInteger("MMMSXLIII");
+		
+	}
 }