Fixed item state management in the UI View

* Fix ActionRow add_item type validation
* Fix View item state tracking
* Fix View add and remove item state
* Add UI view item state tests

tests/test_ui_view.py

@@ -0,0 +1,88 @@
+"""
+The MIT License (MIT)
+
+Copyright (c) 2015-present Rapptz
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+"""
+
+from __future__ import annotations
+
+import discord
+import pytest
+
+
+def test_add_item_with_full_row():
+    view = discord.ui.View()
+
+    for i in range(5):
+        view.add_item(discord.ui.Button(label=str(i), row=0))
+
+    with pytest.raises(ValueError):
+        view.add_item(discord.ui.Button(label="6", row=0))
+
+    assert len(view.children) == 5
+    assert view.total_children_count == 5
+
+
+def test_add_item_invalid():
+    view = discord.ui.View()
+
+    with pytest.raises(TypeError):
+        view.add_item(object())  # type: ignore
+
+
+def test_remove_item():
+    view = discord.ui.View()
+    item = discord.ui.Button(label="Test")
+    view.add_item(item)
+
+    view.remove_item(item)
+
+    assert view.children == []
+    assert view.total_children_count == 0
+    assert item.view is None
+
+
+def test_action_row_add_item_invalid():
+    row = discord.ui.ActionRow()
+
+    with pytest.raises(TypeError):
+        row.add_item(object())  # type: ignore
+
+
+def test_layout_view_add_item_with_too_many_children():
+    view = discord.ui.LayoutView()
+    max_item_limit = 40
+
+    for i in range(max_item_limit - 1):
+        view.add_item(discord.ui.TextDisplay(str(i)))
+
+    row = discord.ui.ActionRow(
+        discord.ui.Button(label="A"),
+        discord.ui.Button(label="B"),
+    )
+
+    with pytest.raises(ValueError):
+        view.add_item(row)
+
+    assert len(view.children) == max_item_limit - 1
+    assert view.total_children_count == max_item_limit - 1
+    assert row.view is None
+    assert all(item.view is None for item in row.children)