the-mews/app/test/fake_fetch.dart

import 'package:actors/actors.dart';

import 'package:mews/application/actors/fetch_actor.dart';
import 'package:mews/mews/atom.dart';
import 'package:mews/mews/parser.dart';

/// Serves pages from an in-memory map without network or isolates, so
/// navigation tests are deterministic. [sources] wins over the cached source
/// a caller offers, the way a server answering 200 does, so a test can change
/// what a site publishes between two fetches. An address with no source is
/// unreachable, and the cached copy stands in for it if there is one.
class FakeFetch implements Actor<FetchCommand, FetchResult> {
  FakeFetch(this.sources, {this.feeds = const {}});

  final Map<String, String> sources;

  /// Atom feeds by address, for sites that publish through one.
  final Map<String, String> feeds;

  @override
  Future<FetchResult> send(FetchCommand message) async {
    return switch (message) {
      ParseSource(:final url, :final source) => _parse(url, source),
      FetchPage(:final url, :final cachedSource) => switch ((
        sources[url],
        cachedSource,
      )) {
        (final String fresh, _) => _parse(url, fresh),
        (null, final String cached) => _parse(url, cached),
        _ => const FetchNetworkError(),
      },
      FetchFeed(:final url) => switch (feeds[url]) {
        final String source =>
          FetchFeedOk(url: url, entries: parseAtomEntries(source: source, feedUrl: url)),
        null => const FetchNetworkError(),
      },
      _ => const FetchNetworkError(),
    };
  }

  FetchResult _parse(String url, String source) {
    try {
      return FetchPageOk(page: parseMewsPage(source: source, url: url), source: source);
    } on MewsParseException catch (e) {
      return FetchParseError(e.message, source);
    }
  }

  @override
  Future<void> close() async {}

  @override
  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}