Add itest_store.py to test file storage

tests/integration/fixtures/testStore.txt

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+Never gonna give you up.

tests/integration/itest_store.py

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+import pytest
+
+from aleph.sdk.client import AuthenticatedAlephHttpClient
+from aleph.sdk.query.filters import MessageFilter
+from tests.integration.toolkit import has_messages, try_until
+
+from .config import REFERENCE_NODE, TARGET_NODE
+
+
+async def create_store_on_target(account, emitter_node: str, receiver_node: str):
+    """
+    Create a POST message on the target node, then fetch it from the reference node and download the file.
+    """
+    with open("tests/integration/fixtures/testStore.txt", "rb") as f:
+        file_content = f.read()
+    async with AuthenticatedAlephHttpClient(
+        account=account, api_server=emitter_node
+    ) as tx_session:
+        store_message, message_status = await tx_session.create_store(
+            file_content=file_content,
+            extra_fields={"test": "test"},
+        )
+
+    async with AuthenticatedAlephHttpClient(
+        account=account, api_server=receiver_node
+    ) as rx_session:
+        responses = await try_until(
+            rx_session.get_messages,
+            has_messages,
+            timeout=5,
+            message_filter=MessageFilter(
+                hashes=[store_message.item_hash],
+            ),
+        )
+
+    message_from_target = responses.messages[0]
+    assert store_message.item_hash == message_from_target.item_hash
+
+    async with AuthenticatedAlephHttpClient(
+        account=account, api_server=receiver_node
+    ) as rx_session:
+        store_content = await rx_session.download_file(store_message.content.item_hash)
+        assert store_content == file_content
+
+
+@pytest.mark.asyncio
+async def test_create_message_on_target(fixture_account):
+    """
+    Attempts to create a new message on the target node and verifies if the message can be fetched from
+    the reference node.
+    """
+    await create_store_on_target(
+        fixture_account, emitter_node=TARGET_NODE, receiver_node=REFERENCE_NODE
+    )
+
+
+@pytest.mark.asyncio
+async def test_create_message_on_reference(fixture_account):
+    """
+    Attempts to create a new message on the reference node and verifies if the message can be fetched from
+    the target node.
+    """
+    await create_store_on_target(
+        fixture_account, emitter_node=REFERENCE_NODE, receiver_node=TARGET_NODE
+    )