Convert JSON with "string enum" properties to interface - json

Question

In our project, we are using string enum, to send the data from the BE to the client. Now the issue is, that when we mock the data, it contains the "enum strings" in the mock json files.
These mock json files are then imported like this: import testJson from '.test.json'; ('resolveJsonModule' is enabled in tsconfig), which gives them a type 'based on the static JSON shape.' (See: Resolve JSON Module).
Now the type which is generated for that enum property is string and not enum, so when I try to cast the json to the interface type, it throws me an error: Type 'string' is not assignable to type 'testEnum'.
Stackblitz example:
const testJSON = {
name: 'hello World',
enumProp: "MYTESTENUM_2",
};
enum testEnum {
MYTESTENUM = "MYTESTENUM",
MYTESTENUM_2 = "MYTESTENUM_2",
}
interface testinterface {
name: string;
enumProp: testEnum;
}
//const castJsonFile: testinterface = testJSON; // not compiling because the "string enums" cannot be converted
const castJsonFile: testinterface = testJSON as any; // any cast is needed, to get it compiling, but looses all type safety
// Write TypeScript code!
const appDiv: HTMLElement = document.getElementById('app');
appDiv.innerHTML = (castJsonFile.enumProp === testEnum.MYTESTENUM_2) as any as string;
Link: https://stackblitz.com/edit/typescript-fjy8zs?file=index.ts
If I would not use "string enums" it would work fine, but this is a change which cannot be done.
Is there a way to tell typescript to treat the "string enums" as enums if he finds such a property in a JSON file?