Combine and refine dependency injection patterns

Author: gyermolenko

patterns/dependency_injection.py

@@ -0,0 +1,104 @@
+#!/usr/bin/python
+# -*- coding : utf-8 -*-
+
+"""
+Port of the Java example of "Constructor Injection" in
+"xUnit Test Patterns - Refactoring Test Code" by Gerard Meszaros
+(ISBN-10: 0131495054, ISBN-13: 978-0131495050)
+
+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
+"""
+
+import datetime
+
+
+class ConstructorInjection(object):
+
+    def __init__(self, time_provider):
+        self.time_provider = time_provider
+
+    def get_current_time_as_html_fragment(self):
+        current_time = self.time_provider()
+        current_time_as_html_fragment = "<span class=\"tinyBoldText\">{}</span>".format(current_time)
+        return current_time_as_html_fragment
+
+
+class ParameterInjection(object):
+
+    def __init__(self):
+        pass
+
+    def get_current_time_as_html_fragment(self, time_provider):
+        current_time = time_provider()
+        current_time_as_html_fragment = "<span class=\"tinyBoldText\">{}</span>".format(current_time)
+        return current_time_as_html_fragment
+
+
+class SetterInjection(object):
+    """Setter Injection"""
+
+    def __init__(self):
+        pass
+
+    def set_time_provider(self, time_provider):
+        self.time_provider = time_provider
+
+    def get_current_time_as_html_fragment(self):
+        current_time = self.time_provider()
+        current_time_as_html_fragment = "<span class=\"tinyBoldText\">{}</span>".format(current_time)
+        return current_time_as_html_fragment
+
+
+def production_code_time_provider():
+    """
+    Production code version of the time provider (just a wrapper for formatting
+    datetime for this example).
+    """
+    current_time = datetime.datetime.now()
+    current_time_formatted = "{}:{}".format(current_time.hour, current_time.minute)
+    return current_time_formatted
+
+
+def midnight_time_provider():
+    """Hard-coded stub"""
+    return "24:01"
+
+
+def main():
+    """
+    >>> time_with_ci1 = ConstructorInjection(midnight_time_provider)
+    >>> time_with_ci1.get_current_time_as_html_fragment()
+    '<span class="tinyBoldText">24:01</span>'
+
+    >>> time_with_ci2 = ConstructorInjection(production_code_time_provider)
+    >>> time_with_ci2.get_current_time_as_html_fragment()
+    '<span class="tinyBoldText">...</span>'
+
+    >>> time_with_pi = ParameterInjection()
+    >>> time_with_pi.get_current_time_as_html_fragment(midnight_time_provider)
+    '<span class="tinyBoldText">24:01</span>'
+
+    >>> time_with_si = SetterInjection()
+
+    # >>> time_with_si.get_current_time_as_html_fragment()
+    # AttributeError: 'SetterInjection' object has no attribute 'time_provider'
+
+    >>> time_with_si.set_time_provider(midnight_time_provider)
+    >>> time_with_si.get_current_time_as_html_fragment()
+    '<span class="tinyBoldText">24:01</span>'
+    """
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod(optionflags=doctest.ELLIPSIS)