diff --git a/tests/test_cloud_api_datasets.py b/tests/test_cloud_api_datasets.py
new file mode 100644
index 0000000..89dcc75
--- /dev/null
+++ b/tests/test_cloud_api_datasets.py
@@ -0,0 +1,86 @@
+"""Unit tests for ndi.cloud.api.datasets — no network required."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import pytest
+
+
+def _make_client(org_id: str = "org-123") -> MagicMock:
+    """Return a mock CloudClient with a config carrying *org_id*."""
+    client = MagicMock()
+    client.config.org_id = org_id
+    client.config.api_url = "https://api.ndi-cloud.com/v1"
+    client.get.return_value = {
+        "datasets": [{"id": "ds-1", "name": "Test"}],
+        "totalNumber": 1,
+    }
+    return client
+
+
+class TestListDatasets:
+    """listDatasets should work with or without an explicit org_id."""
+
+    def test_without_org_id_uses_client_config(self):
+        """Calling listDatasets() with no org_id should resolve it from client config."""
+        from ndi.cloud.api.datasets import listDatasets
+
+        client = _make_client(org_id="org-abc")
+        result = listDatasets(client=client)
+
+        client.get.assert_called_once()
+        call_kwargs = client.get.call_args
+        assert call_kwargs.kwargs["organizationId"] == "org-abc"
+        assert result["datasets"][0]["name"] == "Test"
+
+    def test_with_explicit_org_id(self):
+        """Passing org_id explicitly should use that value."""
+        from ndi.cloud.api.datasets import listDatasets
+
+        client = _make_client(org_id="org-abc")
+        listDatasets("org-explicit", client=client)
+
+        call_kwargs = client.get.call_args
+        assert call_kwargs.kwargs["organizationId"] == "org-explicit"
+
+    def test_no_org_id_and_no_config_raises(self):
+        """If org_id is omitted and client config has none, raise ValueError."""
+        from ndi.cloud.api.datasets import listDatasets
+
+        client = _make_client(org_id="")
+        with pytest.raises(ValueError, match="org_id is required"):
+            listDatasets(client=client)
+
+
+class TestListAllDatasets:
+    """listAllDatasets should work without an explicit org_id."""
+
+    def test_without_org_id(self):
+        from ndi.cloud.api.datasets import listAllDatasets
+
+        client = _make_client(org_id="org-abc")
+        result = listAllDatasets(client=client)
+
+        assert len(result.data) == 1
+
+
+class TestCreateDataset:
+    """createDataset should work without an explicit org_id."""
+
+    def test_without_org_id(self):
+        from ndi.cloud.api.datasets import createDataset
+
+        client = _make_client(org_id="org-abc")
+        client.post.return_value = {"id": "ds-new", "name": "NewDS"}
+        createDataset(name="NewDS", client=client)
+
+        call_kwargs = client.post.call_args
+        assert call_kwargs.kwargs["organizationId"] == "org-abc"
+
+    def test_without_org_id_and_no_config_raises(self):
+        from ndi.cloud.api.datasets import createDataset
+
+        client = _make_client(org_id="")
+        with pytest.raises(ValueError, match="org_id is required"):
+            createDataset(name="NewDS", client=client)