diff --git a/scene/resources/theme.cpp b/scene/resources/theme.cpp
index 373fbb94ea1..be54c309c87 100644
--- a/scene/resources/theme.cpp
+++ b/scene/resources/theme.cpp
@@ -261,6 +261,27 @@ int Theme::get_fallback_font_size() {
 	return fallback_font_size;
 }
 
+bool Theme::is_valid_type_name(const String &p_name) {
+	for (int i = 0; i < p_name.length(); i++) {
+		if (!is_ascii_identifier_char(p_name[i])) {
+			return false;
+		}
+	}
+	return true;
+}
+
+bool Theme::is_valid_item_name(const String &p_name) {
+	if (p_name.is_empty()) {
+		return false;
+	}
+	for (int i = 0; i < p_name.length(); i++) {
+		if (!is_ascii_identifier_char(p_name[i])) {
+			return false;
+		}
+	}
+	return true;
+}
+
 // Fallback values for theme item types, configurable per theme.
 void Theme::set_default_base_scale(float p_base_scale) {
 	if (default_base_scale == p_base_scale) {
@@ -326,6 +347,9 @@ bool Theme::has_default_font_size() const {
 
 // Icons.
 void Theme::set_icon(const StringName &p_name, const StringName &p_theme_type, const Ref<Texture2D> &p_icon) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = false;
 	if (icon_map[p_theme_type].has(p_name) && icon_map[p_theme_type][p_name].is_valid()) {
 		existing = true;
@@ -358,6 +382,8 @@ bool Theme::has_icon_nocheck(const StringName &p_name, const StringName &p_theme
 }
 
 void Theme::rename_icon(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!icon_map.has(p_theme_type), "Cannot rename the icon '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(icon_map[p_theme_type].has(p_name), "Cannot rename the icon '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!icon_map[p_theme_type].has(p_old_name), "Cannot rename the icon '" + String(p_old_name) + "' because it does not exist.");
@@ -396,6 +422,8 @@ void Theme::get_icon_list(StringName p_theme_type, List<StringName> *p_list) con
 }
 
 void Theme::add_icon_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (icon_map.has(p_theme_type)) {
 		return;
 	}
@@ -433,6 +461,9 @@ void Theme::get_icon_type_list(List<StringName> *p_list) const {
 
 // Styleboxes.
 void Theme::set_stylebox(const StringName &p_name, const StringName &p_theme_type, const Ref<StyleBox> &p_style) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = false;
 	if (style_map[p_theme_type].has(p_name) && style_map[p_theme_type][p_name].is_valid()) {
 		existing = true;
@@ -465,6 +496,8 @@ bool Theme::has_stylebox_nocheck(const StringName &p_name, const StringName &p_t
 }
 
 void Theme::rename_stylebox(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!style_map.has(p_theme_type), "Cannot rename the stylebox '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(style_map[p_theme_type].has(p_name), "Cannot rename the stylebox '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!style_map[p_theme_type].has(p_old_name), "Cannot rename the stylebox '" + String(p_old_name) + "' because it does not exist.");
@@ -503,6 +536,8 @@ void Theme::get_stylebox_list(StringName p_theme_type, List<StringName> *p_list)
 }
 
 void Theme::add_stylebox_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (style_map.has(p_theme_type)) {
 		return;
 	}
@@ -540,6 +575,9 @@ void Theme::get_stylebox_type_list(List<StringName> *p_list) const {
 
 // Fonts.
 void Theme::set_font(const StringName &p_name, const StringName &p_theme_type, const Ref<Font> &p_font) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = false;
 	if (font_map[p_theme_type][p_name].is_valid()) {
 		existing = true;
@@ -574,6 +612,8 @@ bool Theme::has_font_nocheck(const StringName &p_name, const StringName &p_theme
 }
 
 void Theme::rename_font(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!font_map.has(p_theme_type), "Cannot rename the font '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(font_map[p_theme_type].has(p_name), "Cannot rename the font '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!font_map[p_theme_type].has(p_old_name), "Cannot rename the font '" + String(p_old_name) + "' because it does not exist.");
@@ -612,6 +652,8 @@ void Theme::get_font_list(StringName p_theme_type, List<StringName> *p_list) con
 }
 
 void Theme::add_font_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (font_map.has(p_theme_type)) {
 		return;
 	}
@@ -649,6 +691,9 @@ void Theme::get_font_type_list(List<StringName> *p_list) const {
 
 // Font sizes.
 void Theme::set_font_size(const StringName &p_name, const StringName &p_theme_type, int p_font_size) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = has_font_size_nocheck(p_name, p_theme_type);
 	font_size_map[p_theme_type][p_name] = p_font_size;
 
@@ -674,6 +719,8 @@ bool Theme::has_font_size_nocheck(const StringName &p_name, const StringName &p_
 }
 
 void Theme::rename_font_size(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!font_size_map.has(p_theme_type), "Cannot rename the font size '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(font_size_map[p_theme_type].has(p_name), "Cannot rename the font size '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!font_size_map[p_theme_type].has(p_old_name), "Cannot rename the font size '" + String(p_old_name) + "' because it does not exist.");
@@ -708,6 +755,8 @@ void Theme::get_font_size_list(StringName p_theme_type, List<StringName> *p_list
 }
 
 void Theme::add_font_size_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (font_size_map.has(p_theme_type)) {
 		return;
 	}
@@ -733,6 +782,9 @@ void Theme::get_font_size_type_list(List<StringName> *p_list) const {
 
 // Colors.
 void Theme::set_color(const StringName &p_name, const StringName &p_theme_type, const Color &p_color) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = has_color_nocheck(p_name, p_theme_type);
 	color_map[p_theme_type][p_name] = p_color;
 
@@ -756,6 +808,8 @@ bool Theme::has_color_nocheck(const StringName &p_name, const StringName &p_them
 }
 
 void Theme::rename_color(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!color_map.has(p_theme_type), "Cannot rename the color '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(color_map[p_theme_type].has(p_name), "Cannot rename the color '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!color_map[p_theme_type].has(p_old_name), "Cannot rename the color '" + String(p_old_name) + "' because it does not exist.");
@@ -790,6 +844,8 @@ void Theme::get_color_list(StringName p_theme_type, List<StringName> *p_list) co
 }
 
 void Theme::add_color_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (color_map.has(p_theme_type)) {
 		return;
 	}
@@ -815,6 +871,9 @@ void Theme::get_color_type_list(List<StringName> *p_list) const {
 
 // Theme constants.
 void Theme::set_constant(const StringName &p_name, const StringName &p_theme_type, int p_constant) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	bool existing = has_constant_nocheck(p_name, p_theme_type);
 	constant_map[p_theme_type][p_name] = p_constant;
 
@@ -838,6 +897,8 @@ bool Theme::has_constant_nocheck(const StringName &p_name, const StringName &p_t
 }
 
 void Theme::rename_constant(const StringName &p_old_name, const StringName &p_name, const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_item_name(p_name), vformat("Invalid item name: '%s'", p_name));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
 	ERR_FAIL_COND_MSG(!constant_map.has(p_theme_type), "Cannot rename the constant '" + String(p_old_name) + "' because the node type '" + String(p_theme_type) + "' does not exist.");
 	ERR_FAIL_COND_MSG(constant_map[p_theme_type].has(p_name), "Cannot rename the constant '" + String(p_old_name) + "' because the new name '" + String(p_name) + "' already exists.");
 	ERR_FAIL_COND_MSG(!constant_map[p_theme_type].has(p_old_name), "Cannot rename the constant '" + String(p_old_name) + "' because it does not exist.");
@@ -872,6 +933,8 @@ void Theme::get_constant_list(StringName p_theme_type, List<StringName> *p_list)
 }
 
 void Theme::add_constant_type(const StringName &p_theme_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+
 	if (constant_map.has(p_theme_type)) {
 		return;
 	}
@@ -1154,6 +1217,8 @@ void Theme::get_theme_item_type_list(DataType p_data_type, List<StringName> *p_l
 
 // Theme type variations.
 void Theme::set_type_variation(const StringName &p_theme_type, const StringName &p_base_type) {
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_theme_type), vformat("Invalid type name: '%s'", p_theme_type));
+	ERR_FAIL_COND_MSG(!is_valid_type_name(p_base_type), vformat("Invalid type name: '%s'", p_base_type));
 	ERR_FAIL_COND_MSG(p_theme_type == StringName(), "An empty theme type cannot be marked as a variation of another type.");
 	ERR_FAIL_COND_MSG(ClassDB::class_exists(p_theme_type), "A type associated with a built-in class cannot be marked as a variation of another type.");
 	ERR_FAIL_COND_MSG(p_base_type == StringName(), "An empty theme type cannot be the base type of a variation. Use clear_type_variation() instead if you want to unmark '" + String(p_theme_type) + "' as a variation.");
diff --git a/scene/resources/theme.h b/scene/resources/theme.h
index 9afe05007d4..f8f1e956343 100644
--- a/scene/resources/theme.h
+++ b/scene/resources/theme.h
@@ -137,6 +137,9 @@ public:
 	static Ref<Font> get_fallback_font();
 	static int get_fallback_font_size();
 
+	static bool is_valid_type_name(const String &p_name);
+	static bool is_valid_item_name(const String &p_name);
+
 	void set_default_base_scale(float p_base_scale);
 	float get_default_base_scale() const;
 	bool has_default_base_scale() const;
diff --git a/tests/scene/test_theme.h b/tests/scene/test_theme.h
new file mode 100644
index 00000000000..fedffc84493
--- /dev/null
+++ b/tests/scene/test_theme.h
@@ -0,0 +1,257 @@
+/*************************************************************************/
+/*  test_theme.h                                                         */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2022 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* 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.                */
+/*************************************************************************/
+
+#ifndef TEST_THEME_H
+#define TEST_THEME_H
+
+#include "scene/resources/theme.h"
+#include "tests/test_tools.h"
+
+#include "thirdparty/doctest/doctest.h"
+
+namespace TestTheme {
+
+class Fixture {
+public:
+	struct DataEntry {
+		Theme::DataType type;
+		Variant value;
+	} const valid_data[Theme::DATA_TYPE_MAX] = {
+		{ Theme::DATA_TYPE_COLOR, Color() },
+		{ Theme::DATA_TYPE_CONSTANT, 42 },
+		{ Theme::DATA_TYPE_FONT, Ref<Font>(memnew(Font)) },
+		{ Theme::DATA_TYPE_FONT_SIZE, 42 },
+		{ Theme::DATA_TYPE_ICON, Ref<Texture>(memnew(ImageTexture)) },
+		{ Theme::DATA_TYPE_STYLEBOX, Ref<StyleBox>(memnew(StyleBoxFlat)) },
+	};
+
+	const StringName valid_item_name = "valid_item_name";
+	const StringName valid_type_name = "ValidTypeName";
+};
+
+TEST_CASE_FIXTURE(Fixture, "[Theme] Good theme type names") {
+	StringName names[] = {
+		"", // Empty name.
+		"CapitalizedName",
+		"snake_cased_name",
+		"42",
+		"_Underscore_",
+	};
+
+	SUBCASE("add_type") {
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->add_type(name);
+			CHECK_FALSE(ed.has_error);
+		}
+	}
+
+	SUBCASE("set_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->set_theme_item(entry.type, valid_item_name, name, entry.value);
+				CHECK_FALSE(ed.has_error);
+			}
+		}
+	}
+
+	SUBCASE("add_theme_item_type") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->add_theme_item_type(entry.type, name);
+				CHECK_FALSE(ed.has_error);
+			}
+		}
+	}
+
+	SUBCASE("set_type_variation") {
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->set_type_variation(valid_type_name, name);
+			CHECK(ed.has_error == (name == StringName()));
+		}
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->set_type_variation(name, valid_type_name);
+			CHECK(ed.has_error == (name == StringName()));
+		}
+	}
+}
+
+TEST_CASE_FIXTURE(Fixture, "[Theme] Bad theme type names") {
+	StringName names[] = {
+		"With/Slash",
+		"With Space",
+		"With@various$symbols!",
+		String::utf8("contains_汉字"),
+	};
+
+	SUBCASE("add_type") {
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->add_type(name);
+			CHECK(ed.has_error);
+		}
+	}
+
+	SUBCASE("set_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->set_theme_item(entry.type, valid_item_name, name, entry.value);
+				CHECK(ed.has_error);
+			}
+		}
+	}
+
+	SUBCASE("add_theme_item_type") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->add_theme_item_type(entry.type, name);
+				CHECK(ed.has_error);
+			}
+		}
+	}
+
+	SUBCASE("set_type_variation") {
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->set_type_variation(valid_type_name, name);
+			CHECK(ed.has_error);
+		}
+		for (const StringName &name : names) {
+			Ref<Theme> theme = memnew(Theme);
+
+			ErrorDetector ed;
+			theme->set_type_variation(name, valid_type_name);
+			CHECK(ed.has_error);
+		}
+	}
+}
+
+TEST_CASE_FIXTURE(Fixture, "[Theme] Good theme item names") {
+	StringName names[] = {
+		"CapitalizedName",
+		"snake_cased_name",
+		"42",
+		"_Underscore_",
+	};
+
+	SUBCASE("set_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->set_theme_item(entry.type, name, valid_type_name, entry.value);
+				CHECK_FALSE(ed.has_error);
+				CHECK(theme->has_theme_item(entry.type, name, valid_type_name));
+			}
+		}
+	}
+
+	SUBCASE("rename_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+				theme->set_theme_item(entry.type, valid_item_name, valid_type_name, entry.value);
+
+				ErrorDetector ed;
+				theme->rename_theme_item(entry.type, valid_item_name, name, valid_type_name);
+				CHECK_FALSE(ed.has_error);
+				CHECK_FALSE(theme->has_theme_item(entry.type, valid_item_name, valid_type_name));
+				CHECK(theme->has_theme_item(entry.type, name, valid_type_name));
+			}
+		}
+	}
+}
+
+TEST_CASE_FIXTURE(Fixture, "[Theme] Bad theme item names") {
+	StringName names[] = {
+		"", // Empty name.
+		"With/Slash",
+		"With Space",
+		"With@various$symbols!",
+		String::utf8("contains_汉字"),
+	};
+
+	SUBCASE("set_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+
+				ErrorDetector ed;
+				theme->set_theme_item(entry.type, name, valid_type_name, entry.value);
+				CHECK(ed.has_error);
+				CHECK_FALSE(theme->has_theme_item(entry.type, name, valid_type_name));
+			}
+		}
+	}
+
+	SUBCASE("rename_theme_item") {
+		for (const StringName &name : names) {
+			for (const DataEntry &entry : valid_data) {
+				Ref<Theme> theme = memnew(Theme);
+				theme->set_theme_item(entry.type, valid_item_name, valid_type_name, entry.value);
+
+				ErrorDetector ed;
+				theme->rename_theme_item(entry.type, valid_item_name, name, valid_type_name);
+				CHECK(ed.has_error);
+				CHECK(theme->has_theme_item(entry.type, valid_item_name, valid_type_name));
+				CHECK_FALSE(theme->has_theme_item(entry.type, name, valid_type_name));
+			}
+		}
+	}
+}
+
+} // namespace TestTheme
+
+#endif // TEST_THEME_H
diff --git a/tests/test_main.cpp b/tests/test_main.cpp
index dc28a98c97c..1328ab10bf7 100644
--- a/tests/test_main.cpp
+++ b/tests/test_main.cpp
@@ -77,6 +77,7 @@
 #include "tests/scene/test_gradient.h"
 #include "tests/scene/test_path_3d.h"
 #include "tests/scene/test_text_edit.h"
+#include "tests/scene/test_theme.h"
 #include "tests/servers/test_text_server.h"
 #include "tests/test_validate_testing.h"