diff --git a/tests/test_transform.py b/tests/test_transform.py
new file mode 100644
index 0000000..ecaaa40
--- /dev/null
+++ b/tests/test_transform.py
@@ -0,0 +1,28 @@
+from current_status import transform
+
+
+def test_preserves_prior_outputs_and_emits_current_status_implementation() -> None:
+    source = {
+        "service_specification": {"name": "monitor"},
+        "target_management_implementation": {"module": "targets"},
+        "endpoint_check_implementation": {"module": "checker"},
+    }
+    output = transform(source)
+
+    for key in source:
+        assert output[key] == source[key]
+        assert output[key] is not source[key]
+    implementation = output["current_status_implementation"]
+    assert implementation["endpoint"] == "GET /targets/{target_id}/status"
+    assert implementation["no_check_yet"]["http_status"] == 200
+    assert implementation["not_found"]["http_status"] == 404
+    assert len(implementation["race_guards"]) == 2
+
+
+def test_rejects_missing_prior_contract_output() -> None:
+    try:
+        transform({})
+    except ValueError as exc:
+        assert str(exc) == "service_specification must be an object"
+    else:
+        raise AssertionError("expected ValueError")