When using Python class and declaring methods with class scope, you need add @classmethod above the method declaration and add 'cls' to the beginning of method signature. Also remember to put the class name before all the class variables that used inside the given method

@classmethod

def from_roman(cls, roman)

These tests are failing for no known reason.

test.assert_equals(RomanNumerals.to_roman(1990), "MCMXC", '1990 should == "MCMXC"')
test.assert_equals(RomanNumerals.from_roman(RomanNumerals.to_roman(1990)), 1990, '1990 should == 1990')

I am unable to see and check the test suite that performs test on the code.

FYI