Python-Design-Patterns parameter_injection
parameter_injection Model
Python-Design-Patterns parameter_injection
# file: 'parameter_injection.py'
#!/usr/bin/python
# -*- coding : utf-8 -*-
import datetime
"""
Port of the Java example of "Parameter Injection" in
"xUnit Test Patterns - Refactoring Test Code" by Gerard Meszaros
(ISBN-10: 0131495054, ISBN-13: 978-0131495050) accessible in outdated version on
http://xunitpatterns.com/Dependency%20Injection.html.
production code which is untestable:
class TimeDisplay(object):
def __init__(self):
self.time_provider = datetime.datetime
def get_current_time_as_html_fragment(self):
current_time = self.time_provider.now()
current_time_as_html_fragment = "<span class=\"tinyBoldText\">{}</span>".format(current_time)
return current_time_as_html_fragment
"""
class TimeDisplay(object):
def __init__(self):
pass
def get_current_time_as_html_fragment(self, time_provider):
current_time = time_provider.now()
current_time_as_html_fragment = "<span class=\"tinyBoldText\">{}</span>".format(current_time)
return current_time_as_html_fragment
class ProductionCodeTimeProvider(object):
"""
Production code version of the time provider (just a wrapper for formatting
datetime for this example).
"""
def now(self):
current_time = datetime.datetime.now()
current_time_formatted = "{}:{}".format(current_time.hour, current_time.minute)
return current_time_formatted
class MidnightTimeProvider(object):
"""
Class implemented as hard-coded stub (in contrast to configurable stub).
"""
def now(self):
current_time_is_always_midnight = "24:01"
return current_time_is_always_midnight
parameter_injection.py
parameter_injection Test
# file: 'test_parameter_injection.py'
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import unittest
from dft.parameter_injection import TimeDisplay, MidnightTimeProvider, ProductionCodeTimeProvider, datetime
"""
Port of the Java example of "Parameter Injection" in
"xUnit Test Patterns - Refactoring Test Code" by Gerard Meszaros
(ISBN-10: 0131495054, ISBN-13: 978-0131495050) accessible in outdated version on
http://xunitpatterns.com/Dependency%20Injection.html.
Test code which will almost always fail (if not exactly 12:01) when untestable
production code (have a look into constructor_injection.py) is used:
def test_display_current_time_at_midnight(self):
class_under_test = TimeDisplay()
expected_time = "24:01"
result = class_under_test.get_current_time_as_as_html_fragment()
self.assertEqual(result, expected_time)
"""
class ParameterInjectionTest(unittest.TestCase):
def test_display_current_time_at_midnight(self):
"""
Would almost always fail (despite of right at/after midnight) if
untestable production code would have been used.
"""
time_provider_stub = MidnightTimeProvider()
class_under_test = TimeDisplay()
expected_time = "<span class=\"tinyBoldText\">24:01</span>"
self.assertEqual(class_under_test.get_current_time_as_html_fragment(time_provider_stub), expected_time)
def test_display_current_time_at_current_time(self):
"""
Just as justification for working example with the time provider used in
production. (Will always pass.)
"""
production_code_time_provider = ProductionCodeTimeProvider()
class_under_test = TimeDisplay()
current_time = datetime.datetime.now()
expected_time = "<span class=\"tinyBoldText\">{}:{}</span>".format(current_time.hour, current_time.minute)
self.assertEqual(
class_under_test.get_current_time_as_html_fragment(production_code_time_provider), expected_time
)
test_parameter_injection.py
