I just wanted to update the answer with current information (Sep 2019).
As Malcon Heck mentioned, using the Record class is preferred.
Looking at xUnit’s Github, I see that a current way to check for lack of exceptions thrown is like this
[Fact]
public async Task CanDeleteAllTempFiles() {
var exception = await Record.ExceptionAsync(() => DocumentService.DeleteAllTempDocuments());
Assert.Null(exception);
}