Assert that a method was called in a Python unit test

Question

Suppose I have the following code in a Python unit test   aw   aps Request  nv1   aw2   aps Request  nv2   aw    Is there an easy way to assert that a particular method  in my case aw Clear    was called during the second line of the test  e g  is there something like this    pseudocode  assertMethodIsCalled aw Clear  lambda  aps Request  nv2   aw

User · Answer

Yes if you are using Python 3 3   You can use the built-in unittest mock to assert method called  For Python 2 6  use the rolling backport Mock  which is the same thing   Here is a quick example in your case   from unittest mock import MagicMock aw   aps Request  nv1   aw Clear   MagicMock   aw2   aps Request  nv2   aw  assert aw Clear called

User · Answer

Yes  I can give you the outline but my Python is a bit rusty and I m too busy to explain in detail   Basically  you need to put a proxy in the method that will call the original  eg    class fred object      def blog self        print  We Blog     class methCallLogger object      def   init   self  meth        self meth   meth     def   call   self  code None        self meth          would also log the fact that it invoked the method    example  f   fred    f blog   methCallLogger f blog    This StackOverflow answer about callable may help you understand the above   In more detail   Although the answer was accepted  due to the interesting discussion with Glenn and having a few minutes free  I wanted to enlarge on my answer     helper class defined elsewhere class methCallLogger object      def   init   self  meth        self meth   meth      self was called   False     def   call   self  code None        self meth        self was called   True   example class fred object      def blog self        print  We Blog   f   fred   g   fred   f blog   methCallLogger f blog  g blog   methCallLogger g blog  f blog   assert f blog was called  assert not g blog was called

User · Answer

I use Mock  which is now unittest mock on py3 3   for this   from mock import patch from PyQt4 import Qt    patch object Qt QMessageBox   aboutQt   def testShowAboutQt self  mock       self win actionAboutQt trigger       self assertTrue mock called    For your case  it could look like this   import mock from mock import patch   def testClearWasCalled self      aw   aps Request  nv1      with patch object aw   Clear   as mock         aw2   aps Request  nv2   aw      mock assert called with 42    or mock assert called once with 42    Mock supports quite a few useful features  including ways to patch an object or module  as well as checking that the right thing was called  etc etc    Caveat emptor   Buyer beware    If you mistype assert called with  to assert called once or assert called wiht  your test may still run  as Mock will think this is a mocked function and happily go along  unless you use autospec true  For more info read assert called once  Threat or Menace

User · Answer

I m not aware of anything built-in   It s pretty simple to implement   class assertMethodIsCalled object       def   init   self  obj  method           self obj   obj         self method   method      def called self   args    kwargs           self method called   True         self orig method  args    kwargs       def   enter   self           self orig method   getattr self obj  self method          setattr self obj  self method  self called          self method called   False      def   exit   self  exc type  exc value  traceback           assert getattr self obj  self method     self called               method  s was modified during assertMethodIsCalled    self method          setattr self obj  self method  self orig method             If an exception was thrown within the block  we ve already failed          if traceback is None              assert self method called                   method  s of  s was not called     self method  self obj   class test object       def a self           print  test      def b self           self a    obj   test   with assertMethodIsCalled obj   a        obj b     This requires that the object itself won t modify self b  which is almost always true

User · Answer

You can mock out aw Clear  either manually or using a testing framework like pymox  Manually  you d do it using something like this   class MyTest TestCase     def testClear        old clear   aw Clear     clear calls   0     aw Clear   lambda  clear calls    1     aps Request  nv2   aw      assert clear calls    1     aw Clear   old clear   Using pymox  you d do it like this   class MyTest mox MoxTestBase     def testClear        aw   self m CreateMock aps Request      aw Clear       self mox ReplayAll       aps Request  nv2   aw

[python] Assert that a method was called in a Python unit test

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