Reorganize file structure of itest cases

Changes:
* Group tests by shared semantics, rather than having all on top level.
* Remove 2 tests in `builtin.rs` (Vector2, VariantArray), already covered through unit-tests and other itests.

Author: Bromeon

itest/rust/src/builtin_test.rs

@@ -5,10 +5,10 @@
  */
 
 use godot::bind::{godot_api, GodotClass};
-use godot::builtin::{varray, Callable, ToVariant, Variant};
-use godot::engine::Object;
+use godot::builtin::inner::InnerCallable;
+use godot::builtin::{varray, Callable, GodotString, StringName, ToVariant, Variant};
+use godot::engine::{Node2D, Object};
 use godot::obj::{Gd, Share};
-use godot::prelude::GodotString;
 
 use crate::framework::itest;
 
@@ -105,3 +105,23 @@ fn callable_call_return() {
     // errors in godot but does not crash
     assert_eq!(callable.callv(varray!["string"]), Variant::nil());
 }
+
+#[itest]
+fn callable_call_engine() {
+    let obj = Node2D::new_alloc();
+    let cb = Callable::from_object_method(obj.share(), "set_position");
+    let inner: InnerCallable = cb.as_inner();
+
+    assert!(!inner.is_null());
+    assert_eq!(inner.get_object_id(), obj.instance_id().to_i64());
+    assert_eq!(inner.get_method(), StringName::from("set_position"));
+
+    // TODO once varargs is available
+    // let pos = Vector2::new(5.0, 7.0);
+    // inner.call(&[pos.to_variant()]);
+    // assert_eq!(obj.get_position(), pos);
+    //
+    // inner.bindv(array);
+
+    obj.free();
+}

itest/rust/src/color_test.rs renamed to itest/rust/src/builtin_tests/color_test.rs

@@ -4,17 +4,22 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-use crate::framework::{expect_panic, itest};
+use std::cmp::Ordering;
+use std::fmt::Display;
+
 use godot::builtin::{
     dict, varray, FromVariant, GodotString, NodePath, StringName, ToVariant, Variant, Vector2,
     Vector3,
 };
+use godot::builtin::{
+    Basis, Dictionary, VariantArray, VariantConversionError, VariantOperator, VariantType,
+};
 use godot::engine::Node2D;
 use godot::obj::InstanceId;
-use godot::prelude::{Basis, Dictionary, VariantArray, VariantConversionError};
-use godot::sys::{GodotFfi, VariantOperator, VariantType};
-use std::cmp::Ordering;
-use std::fmt::{Debug, Display};
+use godot::sys::GodotFfi;
+
+use crate::common::roundtrip;
+use crate::framework::{expect_panic, itest};
 
 const TEST_BASIS: Basis = Basis::from_rows(
     Vector3::new(1.0, 2.0, 3.0),
@@ -408,19 +413,6 @@ fn variant_hash_correct() {
 
 // ----------------------------------------------------------------------------------------------------------------------------------------------
 
-pub(crate) fn roundtrip<T>(value: T)
-where
-    T: FromVariant + ToVariant + PartialEq + Debug,
-{
-    // TODO test other roundtrip (first FromVariant, then ToVariant)
-    // Some values can be represented in Variant, but not in T (e.g. Variant(0i64) -> Option<InstanceId> -> Variant is lossy)
-
-    let variant = value.to_variant();
-    let back = T::try_from_variant(&variant).unwrap();
-
-    assert_eq!(value, back);
-}
-
 fn truncate_bad<T>(original_value: i64)
 where
     T: FromVariant + Display,