Task.WhenAll() not calling function

I have an asynchronous function:

// In a class called DBUtil
public async Task<bool> UpdateRecord(Guid recordId) {
    await recordObj = recordService.Get(recordId);
    await Task.WhenAll(recordService.UpdateRecord(recordId), adminService.NotifyAdmins(recordObj));
    return true;
}

I created a unit test that is supposed to test if calling UpdateRecord() also called recordService.UpdateRecord() and adminService.NotifyAdmins() like:

[TestMethod]
public async Task UpdateRecordWillUpdateAndNotifyAdmins() {
    ...
    await DBUtil.UpdateRecord(record.Id);
    recordService.AssertWasCalled(f => f.UpdateRecord(record.Id));
    adminService..AssertWasCalled(f => f.NotifyAdmins(record));
}

However, it doesn't seem to call the functions. I tried Task.WaitAll() and ran the functions synchronously using RunSynchronously() but got the same results. How do you add blocking to an asynchronous function?