diff --git a/oasst-shared/tests/test_oasst_api_client.py b/oasst-shared/tests/test_oasst_api_client.py
index be757e8f..7092a97e 100644
--- a/oasst-shared/tests/test_oasst_api_client.py
+++ b/oasst-shared/tests/test_oasst_api_client.py
@@ -1,12 +1,20 @@
+from unittest import mock
 from uuid import uuid4
 
+import aiohttp
 import pytest
 from oasst_shared.api_client import OasstApiClient
+from oasst_shared.exceptions import OasstError, OasstErrorCode
 from oasst_shared.schemas import protocol as protocol_schema
 
 
 @pytest.fixture
 def oasst_api_client_mocked():
+    """
+    A an oasst_api_client pointed at the mocked backend.
+    Relies on ./scripts/backend-development/start-mock-server.sh
+    being run.
+    """
     client = OasstApiClient(backend_url="http://localhost:8080", api_key="123")
     yield client
     # TODO The fixture should close this connection, but there seems to be a bug
@@ -15,6 +23,20 @@ def oasst_api_client_mocked():
     # await client.close()
 
 
+@pytest.fixture
+def mock_http_session():
+    yield mock.AsyncMock(spec=aiohttp.ClientSession)
+
+
+@pytest.fixture
+def oasst_api_client_fake_http(mock_http_session):
+    """
+    An oasst_api_client that uses a mocked http session. No real requests are made.
+    """
+    client = OasstApiClient(backend_url="http://localhost:8080", api_key="123", session=mock_http_session)
+    yield client
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize("task_type", protocol_schema.TaskRequestType)
 async def test_can_fetch_task(task_type: protocol_schema.TaskRequestType, oasst_api_client_mocked: OasstApiClient):
@@ -49,3 +71,22 @@ async def test_can_post_interaction(oasst_api_client_mocked: OasstApiClient):
         )
         is not None
     )
+
+
+@pytest.mark.asyncio
+async def test_can_handle_oasst_error_from_api(
+    oasst_api_client_fake_http: OasstApiClient,
+    mock_http_session: mock.AsyncMock,
+):
+    # Return a 400 response with an OasstErrorResponse body
+    response_body = protocol_schema.OasstErrorResponse(
+        error_code=OasstErrorCode.GENERIC_ERROR,
+        message="Some error",
+    ).json()
+    status_code = 400
+
+    mock_http_session.post.return_value.__aenter__.return_value.json.return_value = response_body
+    mock_http_session.post.return_value.__aenter__.return_value.status = status_code
+
+    with pytest.raises(OasstError):
+        await oasst_api_client_fake_http.post("/some-path", data={})