Unit test a nestJS interceptor - unit-testing

Question

My interceptor intercepts a GET request and adds a header to the response based on some conditions.
My Controller
#UseInterceptors(ServiceHeaderInterceptor)
#Get('users')
public async users(
#Query('id') Id: number,
#Query('name') Name: string,
){
const setFlags: MetaFlags = {setCacheHeader: false, setServiceHeader: false};
const data = await this.service.getUsers(id, name, setFlags);
return data;
}
My interceptor looks like this
#Injectable()
export class HeaderInterceptor implements NestInterceptor {
public intercept(
context: ExecutionContext,
next: CallHandler,
): Observable<any> {
return next.handle().pipe(
map((data: { data: DataType, header: 'cache' | 'database' }) => {
const req = context.switchToHttp().getResponse();
if (data.header === 'database') {
res.setHeader('x-api-key', 'pretty secure');
} else {
res.setHeader(xyz, value);
}
return data.data;
}),
);
}
}
This is my test class
const users = [
{
'id': 1,
'name': 'Adam',
},
{
'id': 2,
'name': 'Evan',
},
]
const executionContext: any = {
switchToHttp: jest.fn().mockReturnThis(),
getResponse: jest.fn().mockReturnThis(),
setHeader: jest.fn().mockReturnThis(),
};
const next = {
handle: () => of(users),
};
beforeEach(async () => {
const module: TestingModule = await Test.createTestingModule({
providers: [
{
provide: UserService,
useValue: mock<UserService>(),
},
ServiceHeaderInterceptor,
],
}).compile();
interceptor = module.get(ServiceHeaderInterceptor);
});
it('get users',async () => {
interceptor.intercept(executionContext, next).subscribe({
next: (value) => {
expect(value).toEqual(users);
},
error: (error) => {
throw error;
},
});
});
});
Is there a way to check what my header values are at this point?
I am able to access only the response body and not the headers.
I need to verify if the header I set in the interceptor is available and has the correct value