Add serialization tests for ForbiddenCallableRelation

Author: nchristensen

ConfigSpace/forbidden.pyx

@@ -583,6 +583,11 @@ cdef class ForbiddenCallableRelation(ForbiddenRelation):
     The ForbiddenCallable uses two hyperparameters as input to a
     specified callable, which returns True if the relationship
     between the two hyperparameters is forbidden.
+    
+    A ForbiddenCallableRelation may not be serializable.
+    :func:`ConfigSpace.read_and_write.write` will attempt to pickle and base64 encode
+    the callable with pickle_callables=True. However, the unpicklability
+    of the callable cannot be assured.
 
     >>> from ConfigSpace import ConfigurationSpace, ForbiddenCallableRelation
     >>>

test/read_and_write/test_json.py

@@ -1,7 +1,8 @@
 import os
 import unittest
+from dataclasses import dataclass
 
-from ConfigSpace.forbidden import ForbiddenLessThanRelation
+from ConfigSpace.forbidden import ForbiddenLessThanRelation, ForbiddenCallableRelation
 from ConfigSpace.read_and_write.json import read, write
 from ConfigSpace.read_and_write.pcs import read as read_pcs
 from ConfigSpace.read_and_write.pcs_new import read as read_pcs_new
@@ -12,6 +13,14 @@
 )
 
 
+@dataclass
+class ProductGreaterThan:
+    limit: int
+
+    def __call__(self, a, b):
+        return a*b > self.limit
+
+
 class TestJson(unittest.TestCase):
 
     def test_serialize_forbidden_in_clause(self):
@@ -27,6 +36,10 @@ def test_serialize_forbidden_relation(self):
         cs.add_forbidden_clause(ForbiddenLessThanRelation(a, b))
         write(cs)
 
+        cs.add_forbidden_clause(ForbiddenCallableRelation(a, b, ProductGreaterThan(3)))
+        self.assertRaises(ValueError, write, cs)
+        write(cs, pickle_callables=True)
+
     def test_configspace_with_probabilities(self):
         cs = ConfigurationSpace()
         cs.add_hyperparameter(