How can I mock ECS with moto? - amazon-web-services

Question

I want to create a mock ECS cluster, but it seems not to work properly. Although something is mocked (I don't get a credentials error), it seems not to "save" the cluster.
How can I create a mock cluster with moto?
MVCE
foo.py
import boto3
def print_clusters():
client = boto3.client("ecs")
print(client.list_clusters())
return client.list_clusters()["clusterArns"]
test_foo.py
import boto3
import pytest
from moto import mock_ecs
import foo
#pytest.fixture
def ecs_cluster():
with mock_ecs():
client = boto3.client("ecs", region_name="us-east-1")
response = client.create_cluster(clusterName="test_ecs_cluster")
yield client
def test_foo(ecs_cluster):
assert foo.print_clusters() == ["test_ecs_cluster"]
What happens
$ pytest test_foo.py
Test session starts (platform: linux, Python 3.8.1, pytest 5.3.5, pytest-sugar 0.9.2)
rootdir: /home/math/GitHub
plugins: black-0.3.8, mock-2.0.0, cov-2.8.1, mccabe-1.0, flake8-1.0.4, env-0.6.2, sugar-0.9.2, mypy-0.5.0
collecting ...
―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――― test_foo ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
ecs_cluster = <botocore.client.ECS object at 0x7fe9b0c73580>
def test_foo(ecs_cluster):
> assert foo.print_clusters() == ["test_ecs_cluster"]
E AssertionError: assert [] == ['test_ecs_cluster']
E Right contains one more item: 'test_ecs_cluster'
E Use -v to get the full diff
test_foo.py:19: AssertionError
---------------------------------------------------------------------------------------------------------------------------------- Captured stdout call ----------------------------------------------------------------------------------------------------------------------------------
{'clusterArns': [], 'ResponseMetadata': {'HTTPStatusCode': 200, 'HTTPHeaders': {'server': 'amazon.com'}, 'RetryAttempts': 0}}
test_foo.py ⨯
What I expected
I expected the list of cluster ARNs to have one element (not the one in the assert statement, but an ARN). But the list is empty.

Answer 1

When creating a cluster, you're using a mocked ECS client.
When listing the clusters, you're creating a new ECS client outside the scope of moto.
In other words, you're creating a cluster in memory - but then ask AWS itself for a list of clusters.
You could rewrite the foo-method to use the mocked ECS client:
def print_clusters(client):
print(client.list_clusters())
return client.list_clusters()["clusterArns"]
def test_foo(ecs_cluster):
assert foo.print_clusters(ecs_cluster) == ["test_ecs_cluster"]

Answer 2

def test_foo(ecs_cluster):
assert foo.print_clusters(ecs_cluster) == ["test_ecs_cluster"]
#This will cause you a bug but I have fixed this bug ..so the code looks like this:
def cluster_list(ecs_cluster):
assert ecs.print_clusters(ecs_cluster) == ['arn:aws:ecs:us-east-1:123456789012:cluster/test_ecs_cluster']
#Explination
So basically you have passed the incorrect assert values..assert foo.print_clusters(ecs_cluster) --> this containes cluster arns it is in the form of an array which is ['arn:aws:ecs:us-east-1:123456789012:cluster/test_ecs_cluster'] and you are trying to access the [1] index and testing if its == "test_ecs_cluster" which is wrong so instead to that pass the full arn just to test your code ..