fix: default predicate value on construction

source/modulo_core/include/modulo_core/Predicate.hpp

@@ -12,16 +12,14 @@ namespace modulo_core {
  */
 class Predicate {
 public:
-  explicit Predicate(const std::function<bool(void)>& predicate_function) : predicate_(std::move(predicate_function)) {
-    previous_value_ = !predicate_();
-  }
+  explicit Predicate(const std::function<bool(void)>& predicate_function) : predicate_(std::move(predicate_function)) {}
 
   bool get_value() const { return predicate_(); }
 
   void set_predicate(const std::function<bool(void)>& predicate_function) { predicate_ = predicate_function; }
 
   std::optional<bool> query() {
-    if (const auto new_value = predicate_(); new_value != previous_value_) {
+    if (const auto new_value = predicate_(); !previous_value_ || new_value != *previous_value_) {
       previous_value_ = new_value;
       return new_value;
     }
@@ -30,7 +28,7 @@ class Predicate {
 
 private:
   std::function<bool(void)> predicate_;
-  bool previous_value_;
+  std::optional<bool> previous_value_;
 };
 
 }// namespace modulo_core

source/modulo_core/modulo_core/predicate.py

@@ -9,7 +9,7 @@ def __init__(self, predicate_function: Callable[[], bool]):
         value = predicate_function()
         if not isinstance(value, bool):
             raise CoreError("Predicate function does not return a bool")
-        self.__previous_value = not value
+        self.__previous_value: Optional[bool] = None
 
     def get_value(self) -> bool:
         return self.__predicate()

source/modulo_core/test/cpp/test_predicate.cpp

@@ -25,3 +25,12 @@ TEST(PredicateTest, SimplePredicate) {
   value = predicate.query();
   EXPECT_FALSE(value);
 }
+
+TEST(PredicateTest, ChangeBeforeQuery) {
+  auto predicate = Predicate([]() { return true; });
+  predicate.set_predicate([]() { return false; });
+  EXPECT_FALSE(predicate.get_value());
+  auto value = predicate.query();
+  EXPECT_TRUE(value);
+  EXPECT_FALSE(*value);
+}

source/modulo_core/test/python/test_predicate.py

@@ -0,0 +1,23 @@
+from modulo_core import Predicate
+
+
+def test_simple_predicate():
+    predicate = Predicate(lambda: True)
+    assert predicate.get_value()
+    assert predicate.query()
+    assert predicate.get_value()
+    assert predicate.query() is None
+
+    predicate.set_predicate(lambda: False)
+    assert predicate.get_value() is False
+    assert predicate.query() is False
+    assert predicate.get_value() is False
+    assert predicate.query() is None
+
+
+def test_predicate_change_before_query():
+    predicate = Predicate(lambda: False)
+    predicate.set_predicate(lambda: True)
+    assert predicate.get_value()
+    assert predicate.query()
+    assert predicate.query() is None