diff --git a/lib/roman_numerals.dart b/lib/roman_numerals.dart
index 0cbc072..1309230 100644
--- a/lib/roman_numerals.dart
+++ b/lib/roman_numerals.dart
@@ -1,3 +1,46 @@
-String integerToRoman(int number) {
-  throw UnimplementedError();
+class RomanNumeralInput {
+  static const _minValue = 1;
+  static const _maxValue = 3999;
+
+  final int value;
+
+  RomanNumeralInput(this.value) {
+    if (value < _minValue || value > _maxValue) {
+      throw ArgumentError(
+        'Roman numeral input must be between $_minValue and $_maxValue',
+      );
+    }
+  }
+}
+
+String integerToRoman(int number) {
+  final input = RomanNumeralInput(number);
+
+  const conversionRules = [
+    (1000, 'M'),
+    (900, 'CM'),
+    (500, 'D'),
+    (400, 'CD'),
+    (100, 'C'),
+    (90, 'XC'),
+    (50, 'L'),
+    (40, 'XL'),
+    (10, 'X'),
+    (9, 'IX'),
+    (5, 'V'),
+    (4, 'IV'),
+    (1, 'I'),
+  ];
+
+  final result = StringBuffer();
+  var remaining = input.value;
+
+  for (final (value, symbol) in conversionRules) {
+    while (remaining >= value) {
+      result.write(symbol);
+      remaining -= value;
+    }
+  }
+
+  return result.toString();
 }
diff --git a/test/roman_numerals_test.dart b/test/roman_numerals_test.dart
index ab73b3a..831aa9c 100644
--- a/test/roman_numerals_test.dart
+++ b/test/roman_numerals_test.dart
@@ -1 +1,84 @@
-void main() {}
+import 'package:tdd_katas/roman_numerals.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Roman Numerals Conversion', () {
+    group('Basic Symbols', () {
+      test('smallest unit', () => expect(integerToRoman(1), 'I'));
+      test('five', () => expect(integerToRoman(5), 'V'));
+      test('ten', () => expect(integerToRoman(10), 'X'));
+      test('fifty', () => expect(integerToRoman(50), 'L'));
+      test('hundred', () => expect(integerToRoman(100), 'C'));
+      test('five hundred', () => expect(integerToRoman(500), 'D'));
+      test('thousand', () => expect(integerToRoman(1000), 'M'));
+    });
+
+    group('Subtractive Notation', () {
+      test('four (one before five)', () => expect(integerToRoman(4), 'IV'));
+      test('nine (one before ten)', () => expect(integerToRoman(9), 'IX'));
+      test('forty (ten before fifty)', () => expect(integerToRoman(40), 'XL'));
+      test(
+        'ninety (ten before hundred)',
+        () => expect(integerToRoman(90), 'XC'),
+      );
+      test(
+        'four hundred (hundred before five hundred)',
+        () => expect(integerToRoman(400), 'CD'),
+      );
+      test(
+        'nine hundred (hundred before thousand)',
+        () => expect(integerToRoman(900), 'CM'),
+      );
+    });
+
+    group('Additive Combinations', () {
+      test('two (repeated symbol)', () => expect(integerToRoman(2), 'II'));
+      test(
+        'three (maximum repetition)',
+        () => expect(integerToRoman(3), 'III'),
+      );
+      test('six (additive after five)', () => expect(integerToRoman(6), 'VI'));
+      test(
+        'twenty-seven (multiple symbols)',
+        () => expect(integerToRoman(27), 'XXVII'),
+      );
+    });
+
+    group('Complex Edge Cases', () {
+      test(
+        'forty-nine (combines subtractive symbols)',
+        () => expect(integerToRoman(49), 'XLIX'),
+      );
+      test(
+        'ninety-nine (maximum two-digit complexity)',
+        () => expect(integerToRoman(99), 'XCIX'),
+      );
+      test(
+        'four hundred forty-four (all subtractive positions)',
+        () => expect(integerToRoman(444), 'CDXLIV'),
+      );
+      test(
+        '1994 (year notation stress test)',
+        () => expect(integerToRoman(1994), 'MCMXCIV'),
+      );
+      test(
+        '3999 (maximum valid Roman numeral)',
+        () => expect(integerToRoman(3999), 'MMMCMXCIX'),
+      );
+    });
+
+    group('Error Handling', () {
+      test('rejects zero', () {
+        expect(() => integerToRoman(0), throwsArgumentError);
+      });
+
+      test('rejects negative numbers', () {
+        expect(() => integerToRoman(-5), throwsArgumentError);
+      });
+
+      test('rejects numbers above 3999', () {
+        expect(() => integerToRoman(4000), throwsArgumentError);
+      });
+    });
+  });
+}