Roman Numeral Kata

The Romans wrote their numbers using letters:

• I = 1
• V = 5
• X = 10
• L = 50
• C = 100
• D = 500
• M = 1000

Rules:

• I, X, C, and M can be repeated at most 3 times
• V, L, and D can never be repeated
• I, X, and C (the “1” symbols) can only be subtracted from the next 2 highest values (IV and IX, but not IC)
• Only one subtraction can be made per numeral ('XC' is allowed, 'XXC' is not)
• V, L and D (the “5” symbols) can never be subtracted.

Goal:

Use Test-Driven-Development to write a function which converts arabic to roman numerals.