TS loop properties from Partial<Class> and set it to Class

I have a basic JS class. A very heavily simplified example would be

class Test {
  a: number = 1;
  b: string = 'foo';

  populate(data){
    for (let i in data) {
      this[i] = data[i];
    }
  }
}

So I can basically populate an instance based on JSON data from an API.

const myClass = new Test();
myClass.populate({
  a: 3, 
  b: 'hello world'
});

This all works and is used in production for several years (of course with included hasOwProperty and typeof !== 'undefined' checks and so on).

I would like to properly code this in TypeScript, but I have no idea how, because everything fails. I had so many attempts with no avail, for example:

class Test {
    a: number = 1;
    b: string = 'B';

    populate(data: Partial<Test>){
        for(let i in data){
            const v = data[i as keyof Partial<Test>];
            if(v && Object.prototype.hasOwnProperty.call(this, i)){
                this[i as keyof Test] = v; // error Type 'string' is not assignable to type 'never'.(2322)
            }
        }
    }
}

const a = new Test();
a.populate({
    a: 2,
    b: 'bar'
});

What could I do except a //@ts-ignore and [key: string]: any (I would like to omit anys) to make this working?
Here is my playground

How about this

class Test {
    populate(data: Partial<Test>) {
        Object.assign(this, data);
    }
}

EDIT:

In the case you described, you can try:

for (const [key, value] of Object.entries(data)) {
    if(this.hasOwnProperty(key)) {
        Object.assign(this, { [key]: value });
    }
}

The better solution might be to look into validation libraries, such as zod, so that you can catch that sort of error earlier in your code, before it reaches the populate function.