Can not infer type in child class

[Luke100000]

In this minimal example

---@class Vehicle
---@field public test number
local Vehicle = {}
Vehicle.test = 0.0

---@class Plane: Vehicle
local Plane = {}
Plane.test = Plane.test + 1.0

Plane.test is no longer defined: Can not infer type. Lua Diagnostics.(no-unknown)

Why? Plane.test is a number, because its inherited.

I can redefine my fields in every child class but that escalates in copy pasta.

What am I missing?

And related to the overall issue, how is self defined? Why is init2 not working (Fields cannot be injected into the reference of "Plane" for "test2".), but init1 is fine? Theoretically, it should only by syntactic sugar.

---@class (exact) Vehicle
---@field public test1 number
---@field public test2 number
local Vehicle = {}


---@class (exact) Plane: Vehicle
---@field public init1 fun(self: Plane)
---@field public init2 fun(self: Plane)
local Plane = {}

function Plane.init1(self)
    self.test1 = 1
end

function Plane:init2()
    self.test2 = 1
end

Can someone link me an example of OOP which is generally the most approved way to do so?