🧪 [#4980] Add test for select boxes component with a form variable as…

… a data source

When a select box component has a form variable as data source, the 'properties' and 'required' properties in the JSON schema are currently unfilled, because the 'values' option of the component is an empty list.

Solution is to fetch the corresponding form variable and update the 'properties' and 'required' property in the schema accordingly

src/openforms/forms/tests/test_form_to_json_schema.py

@@ -121,3 +121,44 @@ def test_select_component_with_form_variable_as_data_source(self):
         schema = form_variables_to_json_schema(form, ["select"])
 
         self.assertEqual(schema["properties"]["select"]["enum"], ["A", "B", "C"])
+
+    def test_select_boxes_component_with_form_variable_as_data_source(self):
+        form = FormFactory.create()
+        form_def_1 = FormDefinitionFactory.create(
+            configuration={
+                "components": [
+                    {
+                        "label": "Select Boxes",
+                        "key": "selectBoxes",
+                        "type": "selectboxes",
+                        "openForms": {
+                            "dataSrc": "variable",
+                            "translations": {},
+                            "itemsExpression": {"var": "valuesForSelectBoxes"}
+                        },
+                        "values": []
+                    },
+                ]
+            }
+        )
+        form_step_1 = FormStepFactory.create(form=form, form_definition=form_def_1)
+
+        FormVariableFactory.create(
+            form=form,
+            name="Values for select",
+            key="valuesForSelect",
+            user_defined=True,
+            initial_value=["A", "B", "C"]
+        )
+
+        schema = form_variables_to_json_schema(form, ["selectBoxes"])
+
+        self.assertEqual(
+            schema["properties"]["selectBoxes"]["properties"],
+            {
+                "A": {"type": "boolean"},
+                "B": {"type": "boolean"},
+                "C": {"type": "boolean"},
+            }
+        )
+        self.assertEqual(schema["properties"]["selectBoxes"]["required"], ["A", "B", "C"])