diff --git a/src/doc/user_data_tests.cpp b/src/doc/user_data_tests.cpp
new file mode 100644
index 000000000..4f0b34f6a
--- /dev/null
+++ b/src/doc/user_data_tests.cpp
@@ -0,0 +1,190 @@
+// Aseprite Document Library
+// Copyright (c) 2022 Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <gtest/gtest.h>
+
+#include "doc/user_data.h"
+
+using namespace doc;
+using Variant = UserData::Variant;
+using Fixed = UserData::Fixed;
+using Properties = UserData::Properties;
+
+TEST(CustomProperties, SimpleProperties)
+{
+  UserData data;
+  // Initial data doesn't have any properties
+  EXPECT_TRUE(data.properties().empty());
+
+  data.properties()["boolean"] = Variant{false};
+  data.properties()["char"] = Variant{uint8_t('A')};
+  data.properties()["number16"] = Variant{int16_t(-1024)};
+  data.properties()["number32"] = Variant{int32_t(-5628102)};
+  data.properties()["text"] = Variant{"this is some text"};
+  EXPECT_TRUE(data.properties().size() == 5);
+
+  bool* boolean = std::get_if<bool>(&data.properties()["boolean"]);
+  EXPECT_TRUE(boolean);
+  EXPECT_FALSE(*boolean);
+
+  uint8_t* charac = std::get_if<uint8_t>(&data.properties()["char"]);
+  EXPECT_TRUE(charac);
+  EXPECT_TRUE(*charac == 'A');
+
+  int16_t* number16 = std::get_if<int16_t>(&data.properties()["number16"]);
+  EXPECT_TRUE(number16);
+  EXPECT_TRUE(*number16 == -1024);
+
+  int32_t* number32 = std::get_if<int32_t>(&data.properties()["number32"]);
+  EXPECT_TRUE(number32);
+  EXPECT_TRUE(*number32 == -5628102);
+
+  std::string* text = std::get_if<std::string>(&data.properties()["text"]);
+  EXPECT_TRUE(text);
+  EXPECT_TRUE(*text == "this is some text");
+}
+
+TEST(CustomProperties, ComplexProperties)
+{
+  UserData data;
+  // Add a vector of ints as the "list" custom property.
+  data.properties()["list"] = Variant{
+    std::vector<Variant>{
+      Variant{1},
+      Variant{2},
+      Variant{3}
+    }
+  };
+  // Check that we have one property
+  EXPECT_TRUE(data.properties().size() == 1);
+
+  // Get the "list" vector and check some of its content
+  std::vector<Variant>* list = std::get_if<std::vector<Variant>>(&data.properties()["list"]);
+  EXPECT_TRUE(list);
+  EXPECT_TRUE(list->size() == 3);
+  int* v1 = std::get_if<int>(&(*list)[1]);
+  EXPECT_TRUE(*v1 == 2);
+
+  // Add Point, Size, and Rect properties
+  data.properties()["point"] = Variant{gfx::Point(10,30)};
+  data.properties()["size"] = Variant{gfx::Size(50,20)};
+  data.properties()["rect"] = Variant{gfx::Rect(11,22,33,44)};
+  EXPECT_TRUE(data.properties().size() == 4);
+
+  gfx::Point* point = std::get_if<gfx::Point>(&data.properties()["point"]);
+  EXPECT_TRUE(point);
+  EXPECT_TRUE(point->x == 10 && point->y == 30);
+
+  gfx::Size* size = std::get_if<gfx::Size>(&data.properties()["size"]);
+  EXPECT_TRUE(size);
+  EXPECT_TRUE(size->w == 50 && size->h == 20);
+
+  gfx::Rect* rect = std::get_if<gfx::Rect>(&data.properties()["rect"]);
+  EXPECT_TRUE(rect);
+  EXPECT_TRUE(rect->x == 11 && rect->y == 22);
+  EXPECT_TRUE(rect->w == 33 && rect->h == 44);
+
+  // Add Fixed property
+  data.properties()["fixed"] = Variant{Fixed{fixmath::ftofix(10.5)}};
+  EXPECT_TRUE(data.properties().size() == 5);
+
+  Fixed* fixed = std::get_if<Fixed>(&data.properties()["fixed"]);
+  EXPECT_TRUE(fixed);
+  EXPECT_TRUE(fixed->value == fixmath::ftofix(10.5));
+
+  // Add an object with Properties
+  data.properties()["object"] = Variant{
+    Properties{
+      {"id", Variant{uint16_t(400)}},
+      {"color", Variant{"red"}},
+      {"size", Variant{gfx::Size{25,65}}}
+    }
+  };
+  EXPECT_TRUE(data.properties().size() == 6);
+
+  Properties* object = std::get_if<Properties>(&data.properties()["object"]);
+  EXPECT_TRUE(object);
+
+  uint16_t* id = std::get_if<uint16_t>(&(*object)["id"]);
+  EXPECT_TRUE(id);
+  EXPECT_TRUE(*id == 400);
+
+  std::string* color = std::get_if<std::string>(&(*object)["color"]);
+  EXPECT_TRUE(color);
+  EXPECT_TRUE(*color == "red");
+
+  size = std::get_if<gfx::Size>(&(*object)["size"]);
+  EXPECT_TRUE(size);
+  EXPECT_TRUE(size->w == 25 && size->h == 65);
+
+  // Try to get wrong type
+  gfx::Point* p = std::get_if<gfx::Point>(&data.properties()["rect"]);
+  EXPECT_TRUE(p == nullptr);
+
+  data.properties().erase("rect");
+  data.properties().erase("list");
+  data.properties().erase("point");
+  data.properties().erase("text");
+  data.properties().erase("size");
+  data.properties().erase("object");
+  data.properties().erase("fixed");
+  EXPECT_TRUE(data.properties().size() == 0);
+}
+
+TEST(ExtensionProperties, SimpleProperties)
+{
+  UserData data;
+  EXPECT_TRUE(data.properties().empty());
+  EXPECT_TRUE(data.properties("someExtensionId").empty());
+
+  data.properties("someExtensionId")["boolean"] = Variant{false};
+  data.properties("someExtensionId")["char"] = Variant{uint8_t('A')};
+  data.properties("someExtensionId")["number16"] = Variant{int16_t(-1024)};
+  data.properties()["number32"] = Variant{int32_t(-5628102)};
+  data.properties()["text"] = Variant{"this is some text"};
+  EXPECT_TRUE(data.properties("someExtensionId").size() == 3);
+  EXPECT_TRUE(data.properties().size() == 2);
+
+  bool* boolean = std::get_if<bool>(&data.properties("someExtensionId")["boolean"]);
+  EXPECT_TRUE(boolean);
+  EXPECT_FALSE(*boolean);
+
+  uint8_t* charac = std::get_if<uint8_t>(&data.properties("someExtensionId")["char"]);
+  EXPECT_TRUE(charac);
+  EXPECT_TRUE(*charac == 'A');
+
+  int16_t* number16 = std::get_if<int16_t>(&data.properties("someExtensionId")["number16"]);
+  EXPECT_TRUE(number16);
+  EXPECT_TRUE(*number16 == -1024);
+
+  int32_t* number32 = std::get_if<int32_t>(&data.properties()["number32"]);
+  EXPECT_TRUE(number32);
+  EXPECT_TRUE(*number32 == -5628102);
+
+  std::string* text = std::get_if<std::string>(&data.properties()["text"]);
+  EXPECT_TRUE(text);
+  EXPECT_TRUE(*text == "this is some text");
+
+  data.properties().erase("number32");
+  data.properties().erase("text");
+  EXPECT_TRUE(data.properties().size() == 0);
+  EXPECT_TRUE(data.properties("someExtensionId").size() == 3);
+
+  data.properties("someExtensionId").erase("number16");
+  data.properties("someExtensionId").erase("boolean");
+  data.properties("someExtensionId").erase("char");
+  EXPECT_TRUE(data.properties("someExtensionId").size() == 0);
+}
+
+int main(int argc, char** argv)
+{
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}