How to mock a boto3 client object/call

Question

I'm trying to mock one particular boto3 function. My module, Cleanup, imports boto3. Cleanup also has a class, "cleaner". During init, cleaner creates an ec2 client:

self.ec2_client = boto3.client('ec2')

I want to mock the ec2 client method: desribe_tags(), which python says is:

<bound method EC2.describe_tags of <botocore.client.EC2 object at 0x7fd98660add0>>

the furthest I've gotten is importing botocore in my test file and trying:

mock.patch(Cleaner.botocore.client.EC2.describe_tags)

which fails with:

AttributeError: 'module' object has no attribute 'EC2'

How do I mock this method?

Cleanup looks like:

import boto3
class cleaner(object):
    def __init__(self):
        self.ec2_client = boto3.client('ec2')

The ec2_client object is the one that has the desribe_tags() method. It's a botocore.client.EC2 object, but I never directly import botocore.

Answer 1

You should be mocking with respect to where you are testing. So, if you are testing your cleaner class (Which I suggest you use PEP8 standards here, and make it Cleaner), then you want to mock with respect to where you are testing. So, your patching should actually be something along the lines of:

class SomeTest(Unittest.TestCase):
    @mock.patch('path.to.Cleaner.boto3.client', return_value=Mock())
    def setUp(self, boto_client_mock):
        self.cleaner_client = boto_client_mock.return_value

    def your_test(self):
        # call the method you are looking to test here

        # simple test to check that the method you are looking to mock was called
        self.cleaner_client.desribe_tags.assert_called_with()

I suggest reading through the mocking documentation which has many examples to do what you are trying to do