Test registering example custom derived quantity

tests/test_derived_quantities.py

@@ -5,6 +5,8 @@
 
 from pandas.testing import assert_frame_equal
 
+from mikeio1d import Res1D
+
 NODE_DERIVED_QUANTITIES = [
     "NodeFlooding",
     "NodeWaterDepth",
@@ -110,11 +112,36 @@ def test_read_derived_quantities_single_location_reach(res1d_network, reach_deri
 
 def set_multiindex_level_values(df, level, value):
     """Set all values of a MultiIndex level to a specific value."""
-    num_columns = df.shape[1]
-    df.columns = df.columns.set_levels([value for _ in range(num_columns)], level=level)
+    df.columns = df.columns.set_levels([value], level=level)
     return df
 
 
+def test_example_custom_derived_quantity(res1d_network):
+    from mikeio1d.quantities.derived.derived_quantity_example import ExampleDerivedQuantity
+    from mikeio1d.res1d import derived_quantity_manager as dqm
+
+    dqm.register(ExampleDerivedQuantity)
+    res1d_network = Res1D(res1d_network.file_path)
+
+    assert "WaterLevelPlusOne" in res1d_network.derived_quantities
+    assert "WaterLevelPlusOne" in res1d_network.nodes.derived_quantities
+    assert "WaterLevelPlusOne" in res1d_network.reaches.derived_quantities
+
+    df_nodes = res1d_network.nodes.WaterLevelPlusOne.read()
+    df_nodes_expected = res1d_network.nodes.WaterLevel.read(column_mode="compact") + 1
+    df_nodes_expected = set_multiindex_level_values(
+        df_nodes_expected, "quantity", "WaterLevelPlusOne"
+    )
+    assert_frame_equal(df_nodes, df_nodes_expected)
+
+    df_reaches = res1d_network.reaches.WaterLevelPlusOne.read()
+    df_reaches_expected = res1d_network.reaches.WaterLevel.read(column_mode="compact") + 1
+    df_reaches_expected = set_multiindex_level_values(
+        df_reaches_expected, "quantity", "WaterLevelPlusOne"
+    )
+    assert_frame_equal(df_reaches, df_reaches_expected)
+
+
 class TestSpecificDerivedQuantities:
     def test_node_flooding(self, res1d_network):
         df = res1d_network.nodes["1"].NodeFlooding.read()