Python Integration Test Cloud Functions with Server running in subprocess - python-3.x

Question

I am trying to mock a cloud storage response while testing a cloud function in a local testing environment.
1. I am starting the server - as advised by the docs - using a subprocess:
subprocess.Popen(
[
"functions-framework",
"--target",
"my_target",
"--port",
"8080",
"--source",
f"{os.getcwd()}/src/main.py",
],
cwd=os.path.dirname(__file__),
stdout=subprocess.PIPE,
)
2. I then ping the local server from my test function:
res = requests.get(
f"{SETTINGS.BASE_URL}:8080/test",
)
The server is up and running and it works just fine...
The cloud function talks to a Cloud Storage bucket that serves as a "database". However, I do not want to call it and Mock the buckets behaviour. I have tried many different things, such as patching the function, using MagicMock etc.. Nothing works. It always pings the real, live Cloud Storage bucket. I think I am not quite getting how to patch the cloud storage behaviour in the subprocess that the server is using.
Any ideas?
I tried e.g.:
def test_return_from_cs(cls):
mock_client = MagicMock(spec=google.cloud.storage.Client)
# Create a mock bucket
mock_bucket = MagicMock(spec=google.cloud.storage.Bucket)
# Create a mock blob
mock_blob = MagicMock(spec=google.cloud.storage.Blob)
# Set the return value of the mock client's get_bucket method to be the mock bucket
mock_client.get_bucket.return_value = mock_bucket
# Set the return value of the mock bucket's get_blob method to be the mock blob
mock_bucket.get_blob.return_value = mock_blob
# Set the return value of the mock blob's download_as_string method to be a string "test_data"
mock_blob.download_as_string.return_value = "test_data"
import subprocess
import os
subprocess.Popen(
[
"functions-framework",
"--target",
"my_target",
"--port",
"9090",
"--source",
f"{os.getcwd()}/src/main.py",
],
cwd=os.path.dirname(__file__),
stdout=subprocess.PIPE,
)
res = requests.get(
f"{SETTINGS.BASE_URL}:9090/test",
)
assert res.text == "test_data"
subprocess.terminate()
I also tried:
#patch("src.my_module.main.storage.Client", autospec=True)
def test_return_from_cs(cls, clientMock):
blob_mock = (
clientMock().get_bucket.return_value.get_blob.return_value
) # split this up for readability
bucket_mock = blob_mock.get_blob.return_value
bucket_mock.download_as_string.return_value = "test"
res = cls.session.get(
f"{SETTINGS.BASE_URL}:{SETTINGS.PORT}/test",
)
assert res.text == "test"
In the second attempt above the server is already running and imported from a conftest.py.
I guess I do not understand how to mock the call to CS within the subprocess...
It always pings the actual cloud storage bucket...