diff --git a/src/RomanNumerals.java b/src/RomanNumerals.java
index 20904f0..43665df 100644
--- a/src/RomanNumerals.java
+++ b/src/RomanNumerals.java
@@ -1,8 +1,96 @@
 
 public class RomanNumerals {
 	public int convertToInteger(String romanNum) {
-		// To be Implemented
-		return 0;
 		
+		// total num
+		// -> return this
+		int num = 0;
+		
+		// to avoid input errors 
+		// just upper case everything
+		romanNum = romanNum.toUpperCase();
+		
+		// save the string to character array.
+		char[] charArr = romanNum.toCharArray();
+		
+		// loop through the whole array.
+		for(int i = 0; i < romanNum.length(); i++) {
+		
+			// current character
+			char c = charArr[i];
+			
+			switch(c) {
+			
+			// 1
+			case 'I':
+				try {
+					char next_c = charArr[i+1];
+					
+					if(next_c == 'V' || next_c == 'X') {
+						num -= 1;
+					} else {
+						num += 1;
+					}
+				} catch (ArrayIndexOutOfBoundsException e) {
+					num += 1;
+				}
+				break;
+			
+			// 10
+			case 'X':
+				try {
+					char next_c = charArr[i+1];
+					
+					if(next_c == 'L' || next_c == 'C') {
+						num -= 10;
+					} else {
+						num += 10;
+					}
+				} catch (ArrayIndexOutOfBoundsException e) {
+					num += 10;
+				}
+				break;
+				
+			// 100
+			case 'C':
+				try {
+					char next_c = charArr[i+1];
+					
+					if(next_c == 'D' || next_c == 'M') {
+						num -= 100;
+					} else {
+						num += 100;
+					}
+				} catch (ArrayIndexOutOfBoundsException e) {
+					num += 100;
+				}
+				break;
+				
+			// 1000
+			case 'M':
+				num += 1000;
+				break;
+				
+			// 5
+			case 'V':
+				num += 5;
+				break;
+			
+			// 50
+			case 'L':
+				num += 50;
+				break;
+				
+			// 500
+			case 'D':
+				num += 500;
+				break;
+			
+			// invalid
+			default:
+				break;
+			}
+		}
+		return num;
 	}
 }
diff --git a/tests/TestRomanNumerals.java b/tests/TestRomanNumerals.java
index 5d1de75..d416acb 100644
--- a/tests/TestRomanNumerals.java
+++ b/tests/TestRomanNumerals.java
@@ -4,9 +4,91 @@
 
 public class TestRomanNumerals {
 
+	RomanNumerals rn = new RomanNumerals();
+	
 	@Test
-	public void test() {
-		fail("Not yet implemented");
+	public void test_RomanNumerals_notNull() {
+		assertNotNull(rn);
 	}
 
+	@Test
+	public void test_RomanNumerals_return_one() {
+		assertEquals(1, rn.convertToInteger("i"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_two() {
+		assertEquals(2, rn.convertToInteger("ii"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_three() {
+		assertEquals(3, rn.convertToInteger("iii"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_four() {
+		assertEquals(4, rn.convertToInteger("iv"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_five() {
+		assertEquals(5, rn.convertToInteger("v"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_six() {
+		assertEquals(6, rn.convertToInteger("vi"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_seven() {
+		assertEquals(7, rn.convertToInteger("vii"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_eight() {
+		assertEquals(8, rn.convertToInteger("viii"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_nine() {
+		assertEquals(9, rn.convertToInteger("ix"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_ten() {
+		assertEquals(10, rn.convertToInteger("x"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_nineteen() {
+		assertEquals(19, rn.convertToInteger("ixx"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_twenty() {
+		assertEquals(20, rn.convertToInteger("xx"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_ninetyNine() {
+		assertEquals(99, rn.convertToInteger("XCIX"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_999() {
+		assertEquals(999, rn.convertToInteger("CMXCIX"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_1984() {
+		assertEquals(1984, rn.convertToInteger("mcmlxxxiv"));
+	}
+	
+	@Test
+	public void test_RomanNumerals_return_2014() {
+		assertEquals(2014, rn.convertToInteger("mmxiv"));
+	}
+	
 }