Now that the unit tests are complete, it's time to start writing the code that the test cases are attempting to test. You're
going to do this in stages, so you can see all the unit tests fail, then watch them pass one by one as you fill in the gaps
in roman.py.
Example 14.1. roman1.py
This file is available in py/roman/stage1/ in the examples directory.
"""Convert to and from Roman numerals"""#Define exceptionsclass RomanError(Exception): pass
class OutOfRangeError(RomanError): pass
class NotIntegerError(RomanError): passclass InvalidRomanNumeralError(RomanError): passdef toRoman(n):
"""convert integer to Roman numeral"""passdef fromRoman(s):
"""convert Roman numeral to integer"""pass
This is how you define your own custom exceptions in Python. Exceptions are classes, and you create your own by subclassing existing exceptions. It is strongly recommended (but not
required) that you subclass Exception, which is the base class that all built-in exceptions inherit from. Here I am defining RomanError (inherited from Exception) to act as the base class for all my other custom exceptions to follow. This is a matter of style; I could just as easily
have inherited each individual exception from the Exception class directly.
The OutOfRangeError and NotIntegerError exceptions will eventually be used by toRoman to flag various forms of invalid input, as specified in ToRomanBadInput.
The InvalidRomanNumeralError exception will eventually be used by fromRoman to flag invalid input, as specified in FromRomanBadInput.
At this stage, you want to define the API of each of your functions, but you don't want to code them yet, so you stub them out using the Python reserved word pass.
Now for the big moment (drum roll please): you're finally going to run the unit test against this stubby little module. At
this point, every test case should fail. In fact, if any test case passes in stage 1, you should go back to romantest.py and re-evaluate why you coded a test so useless that it passes with do-nothing functions.
Run romantest1.py with the -v command-line option, which will give more verbose output so you can see exactly what's going on as each test case runs.
With any luck, your output should look like this:
Example 14.2. Output of romantest1.py against roman1.py
fromRoman should only accept uppercase input ... ERROR
toRoman should always return uppercase ... ERROR
fromRoman should fail with malformed antecedents ... FAIL
fromRoman should fail with repeated pairs of numerals ... FAIL
fromRoman should fail with too many repeated numerals ... FAIL
fromRoman should give known result with known input ... FAIL
toRoman should give known result with known input ... FAIL
fromRoman(toRoman(n))==n for all n ... FAIL
toRoman should fail with non-integer input ... FAIL
toRoman should fail with negative input ... FAIL
toRoman should fail with large input ... FAIL
toRoman should fail with 0 input ... FAIL
======================================================================
ERROR: fromRoman should only accept uppercase input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 154, in testFromRomanCase
roman1.fromRoman(numeral.upper())
AttributeError: 'None' object has no attribute 'upper'
======================================================================
ERROR: toRoman should always return uppercase
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 148, in testToRomanCase
self.assertEqual(numeral, numeral.upper())
AttributeError: 'None' object has no attribute 'upper'
======================================================================
FAIL: fromRoman should fail with malformed antecedents
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 133, in testMalformedAntecedent
self.assertRaises(roman1.InvalidRomanNumeralError, roman1.fromRoman, s)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: InvalidRomanNumeralError
======================================================================
FAIL: fromRoman should fail with repeated pairs of numerals
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 127, in testRepeatedPairs
self.assertRaises(roman1.InvalidRomanNumeralError, roman1.fromRoman, s)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: InvalidRomanNumeralError
======================================================================
FAIL: fromRoman should fail with too many repeated numerals
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 122, in testTooManyRepeatedNumerals
self.assertRaises(roman1.InvalidRomanNumeralError, roman1.fromRoman, s)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: InvalidRomanNumeralError
======================================================================
FAIL: fromRoman should give known result with known input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 99, in testFromRomanKnownValues
self.assertEqual(integer, result)
File "c:\python21\lib\unittest.py", line 273, in failUnlessEqual
raise self.failureException, (msg or '%s != %s' % (first, second))
AssertionError: 1 != None
======================================================================
FAIL: toRoman should give known result with known input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 93, in testToRomanKnownValues
self.assertEqual(numeral, result)
File "c:\python21\lib\unittest.py", line 273, in failUnlessEqual
raise self.failureException, (msg or '%s != %s' % (first, second))
AssertionError: I != None
======================================================================
FAIL: fromRoman(toRoman(n))==n for all n
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 141, in testSanity
self.assertEqual(integer, result)
File "c:\python21\lib\unittest.py", line 273, in failUnlessEqual
raise self.failureException, (msg or '%s != %s' % (first, second))
AssertionError: 1 != None
======================================================================
FAIL: toRoman should fail with non-integer input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 116, in testNonInteger
self.assertRaises(roman1.NotIntegerError, roman1.toRoman, 0.5)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: NotIntegerError
======================================================================
FAIL: toRoman should fail with negative input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 112, in testNegative
self.assertRaises(roman1.OutOfRangeError, roman1.toRoman, -1)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
======================================================================
FAIL: toRoman should fail with large input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 104, in testTooLarge
self.assertRaises(roman1.OutOfRangeError, roman1.toRoman, 4000)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
======================================================================
FAIL: toRoman should fail with 0 input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage1\romantest1.py", line 108, in testZero
self.assertRaises(roman1.OutOfRangeError, roman1.toRoman, 0)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
----------------------------------------------------------------------
Ran 12 tests in 0.040s
FAILED (failures=10, errors=2)
Running the script runs unittest.main(), which runs each test case, which is to say each method defined in each class within romantest.py. For each test case, it prints out the doc string of the method and whether that test passed or failed. As expected, none of the test cases passed.
For each failed test case, unittest displays the trace information showing exactly what happened. In this case, the call to assertRaises (also called failUnlessRaises) raised an AssertionError because it was expecting toRoman to raise an OutOfRangeError and it didn't.
After the detail, unittest displays a summary of how many tests were performed and how long it took.
Overall, the unit test failed because at least one test case did not pass. When a test case doesn't pass, unittest distinguishes between failures and errors. A failure is a call to an assertXYZ method, like assertEqual or assertRaises, that fails because the asserted condition is not true or the expected exception was not raised. An error is any other sort
of exception raised in the code you're testing or the unit test case itself. For instance, the testFromRomanCase method (“fromRoman should only accept uppercase input”) was an error, because the call to numeral.upper() raised an AttributeError exception, because toRoman was supposed to return a string but didn't. But testZero (“toRoman should fail with 0 input”) was a failure, because the call to fromRoman did not raise the InvalidRomanNumeral exception that assertRaises was looking for.
