How to write test cases for a function which is returning another lamda function in angular ?

Question

mapAsset (nodes, displayName: Array<string>) {
return nodes.map(({ children, ...child }: any) => {

const names = [...displayName, child.name];
Return {
... child,
displayName : names ,
children : this.mapAsset ( children || [] , [ ...names] ) ,
};
});
}