Add test

tests/nexus/test_mpccd_nexus.py

@@ -0,0 +1,24 @@
+from __future__ import annotations
+
+import dxtbx
+
+
+def test_mpccd_nexus_gain(dials_data):
+    """
+    Tests SACLA MPCCD image from CXI.DB 221
+    Includs parameter data_scale_factor, which accounts for a gain of 10
+    """
+
+    try:
+        h5path = (
+            dials_data("image_examples", pathlib=True)
+            / "SACLA-MPCCD-run197287-0-nexus.h5"
+        )
+    except Exception as e:
+        print(type(e), str(e))
+        raise
+    img = dxtbx.load(h5path)
+
+    d = img.get_detector()
+
+    assert d[0].get_gain() == 10