diff --git a/unit-testing.html b/unit-testing.html index 73c5e70..8228217 100755 --- a/unit-testing.html +++ b/unit-testing.html @@ -618,6 +618,8 @@ FAILED (errors=2) def from_roman(s): '''convert Roman numeral to integer''' +

(Hey, did you notice that? I defined a function with nothing but a docstring. That’s legal Python. In fact, some programmers swear by it. “Don’t stub; document!”) +

Now the test cases will actually fail. 

@@ -706,11 +708,11 @@ OK

As you saw in Case Study: Roman Numerals, there are several simple rules for constructing a Roman numeral, using the letters M, D, C, L, X, V, and I. Let's review the rules:

    -
  1. Characters are additive. I is 1, II is 2, and III is 3. VI is 6 (literally, “5 and 1”), VII is 7, and VIII is 8. +
  2. Sometimes characters are additive. I is 1, II is 2, and III is 3. VI is 6 (literally, “5 and 1”), VII is 7, and VIII is 8.
  3. The tens characters (I, X, C, and M) can be repeated up to three times. At 4, you need to subtract from the next highest fives character. You can't represent 4 as IIII; instead, it is represented as IV (“1 less than 5”). 40 is written as XL (“10 less than 50”), 41 as XLI, 42 as XLII, 43 as XLIII, and then 44 as XLIV (“10 less than 50, then 1 less than 5”). -
  4. Similarly, at 9, you need to subtract from the next highest tens character: 8 is VIII, but 9 is IX (“1 less than 10”), not VIIII (since the I character can not be repeated four times). 90 is XC, 900 is CM. +
  5. Sometimes characters are… the opposite of additive. By putting certain characters before others, you subtract from the final value. For example, at 9, you need to subtract from the next highest tens character: 8 is VIII, but 9 is IX (“1 less than 10”), not VIIII (since the I character can not be repeated four times). 90 is XC, 900 is CM.
  6. The fives characters can not be repeated. 10 is always represented as X, never as VV. 100 is always C, never LL. -
  7. Roman numerals are always written highest to lowest, and read left to right, so order of characters matters very much. DC is 600; CD is a completely different number (400, “100 less than 500”). CI is 101; IC is not even a valid Roman numeral (because you can't subtract 1 directly from 100; you would need to write it as XCIX, “10 less than 100, then 1 less than 10”). +
  8. Roman numerals are read left to right, so the order of characters matters very much. DC is 600; CD is a completely different number (400, “100 less than 500”). CI is 101; IC is not even a valid Roman numeral (because you can't subtract 1 directly from 100; you would need to write it as XCIX, “10 less than 100, then 1 less than 10”).

Thus, one useful test would be to ensure that the from_roman() function should fail when you pass it a string with too many repeated numerals. How many is “too many” depends on the numeral. @@ -728,7 +730,7 @@ OK for s in ('CMCM', 'CDCD', 'XCXC', 'XLXL', 'IXIX', 'IVIV'): self.assertRaises(roman6.InvalidRomanNumeralError, roman6.from_roman, s) -

A third test could check that numerals appear in the correct order, from highest to lowest value. For example, CL is 150, but LC is never valid, because the numeral for 50 can never come before the numeral for 100. +

A third test could check that numerals appear in the correct order, from highest to lowest value. For example, CL is 150, but LC is never valid, because the numeral for 50 can never come before the numeral for 100. This test includes a randomly chosen set of invalid antecedents: I before M, V before X, and so on. 

    def test_malformed_antecedents(self):
         '''from_roman should fail with malformed antecedents'''