added failing test for select_subnet with switch results

CHANGELOG.rst

@@ -3,6 +3,7 @@ Change Log
 
 [upcoming release] - 2024-..-..
 -------------------------------
+- [FIXED] handling of switch results in :code:`pp.toolbox.select_subnet`
 - [ADDED] DERController with multiple options to define DER reactive power provision depending on P and V
 - [ADDED] switch results p and q
 - [ADDED] PowerFactory converter: option to export lines with sections as a single line with averaged-out impedance, or export line sections as separate individual lines

pandapower/test/toolbox/test_grid_modification.py

@@ -243,6 +243,15 @@ def test_select_subnet():
     subnet = pp.select_subnet(net2, buses | elements)
     assert net2.switch[net2.switch.et == 'b'].index.isin(subnet.switch.index).all()
 
+    pp.runpp(net2)
+    net3 = pp.select_subnet(net2, [0, 1], include_results=True)
+    assert len(net3.res_switch) > 0
+    assert net3.switch.index.equals(net3.res_switch.index)
+
+    net3 = pp.select_subnet(net2, [0, 1], include_results=True, keep_everything_else=True)
+    assert len(net3.res_switch) > 0
+    assert net3.switch.index.equals(net3.res_switch.index)
+
 
 def test_add_zones_to_elements():
     net = nw.create_cigre_network_mv()