Refactor if X is None

Reproducer

$ pip install nose
$ pip install https://github.com/sixty-north/cosmic-ray/zipball/master

$ cosmic-ray run --test-runner nose --baseline=10 example.json hello.py -- test_hello.py
$ cosmic-ray report example.json

job ID 4:Outcome.SURVIVED:hello
command: cosmic-ray worker hello replace_Is_with_Eq 0 nose -- -v test_hello.py
--- mutation diff ---
--- a/example_06/hello.py
+++ b/example_06/hello.py
@@ -1,7 +1,7 @@


 def sayHello(name, title=None):
-    if (title is None):
+    if (title == None):
         title = 'Mr.'
     return ('Hello %s %s' % (title, name))

total jobs: 9
complete: 9 (100.00%)
survival rate: 11.11%

Note

Since PR #162 Cosmic-Ray skips mutations of the kind == -> is but doesn’t skip the opposite of is -> ==!

Now compare the results after refactoring

$ cosmic-ray run --test-runner nose --baseline=10 example.json hello2.py -- test_hello2.py
$ cosmic-ray report example.json --full-report
total jobs: 0
no jobs completed

Functionality is the same but we have reduced the number of possible mutations!

Source code

hello.py

def sayHello(name, title=None):
    if title is None:
        title = "Mr."

    return "Hello %s %s" % (title, name)

test_hello.py

import hello
import unittest

class TestHello(unittest.TestCase):
    def test_sayHello_without_title(self):
        result = hello.sayHello("Senko")
        self.assertEqual(result, "Hello Mr. Senko")

    def test_sayHello_with_title(self):
        result = hello.sayHello("Senko", title="The Misterious")
        self.assertEqual(result, "Hello The Misterious Senko")


if __name__ == "__main__":
    unittest.main()

hello2.py

def sayHello(name, title=None):
    if not title:
        title = "Mr."

    return "Hello %s %s" % (title, name)

test_hello2.py

import hello
import unittest

class TestHello(unittest.TestCase):
    def test_sayHello_without_title(self):
        result = hello.sayHello("Senko")
        self.assertEqual(result, "Hello Mr. Senko")

    def test_sayHello_with_title(self):
        result = hello.sayHello("Senko", title="The Misterious")
        self.assertEqual(result, "Hello The Misterious Senko")


if __name__ == "__main__":
    unittest.main()