RED: test convert 1 to I

test/roman_numerals_test.dart

@@ -1 +1,8 @@
-void main() {}
+import 'package:tdd_katas/roman_numerals.dart' as roman_numerals;
+import 'package:test/test.dart';
+
+void main() {
+  test('converts 1 to I', () {
+    expect(roman_numerals.integerToRoman(1), 'I');
+  });
+}