Writing some tests, namely the fake game server

tests/FakeGameServer/Options.cs

@@ -0,0 +1,86 @@
+
+using System.Globalization;
+
+namespace FakeGameServer;
+
+internal enum FakeMode
+{
+    Normal,
+    NoReady,
+    FailOnStart,
+    CrashAfterReady,
+    IgnoreStop,
+    IgnoreAll,
+}
+
+internal sealed record FakeSettings(
+    FakeMode Mode,
+    int StartupMs,
+    int StopMs,
+    int CrashAfterMs,
+    int CrashExitCode,
+    bool StdinEofStopsServer)
+{
+    public static FakeSettings FromEnvironment()
+    {
+        var mode = Enum.TryParse<FakeMode>(Env("FAKE_MODE"), true, out var parsed) ? parsed : FakeMode.Normal;
+        return new FakeSettings(
+            mode,
+            EnvInt("FAKE_STARTUP_MS", 500),
+            EnvInt("FAKE_STOP_MS", 200),
+            EnvInt("FAKE_CRASH_AFTER_MS", 300),
+            EnvInt("FAKE_CRASH_EXIT_CODE", 0),
+            string.Equals(Env("FAKE_STDIN_EOF"), "stop", StringComparison.OrdinalIgnoreCase));
+    }
+
+    private static string? Env(string name) => Environment.GetEnvironmentVariable(name);
+
+    private static int EnvInt(string name, int fallback) =>
+        int.TryParse(Env(name), NumberStyles.Integer, CultureInfo.InvariantCulture, out var value)
+            ? value
+            : fallback;
+}
+
+internal sealed record CommandLine(string? DataPath, int? Port, string? SetConfig)
+{
+    // Flags that take a value. Like the real game, the next token is taken as the value
+    // when there is no "=", even if that token is another flag.
+    private static readonly HashSet<string> ValueOptions = new(StringComparer.OrdinalIgnoreCase)
+    {
+        "dataPath", "port", "setconfig", "withconfig", "logPath", "ip", "maxclients",
+    };
+
+    public static CommandLine Parse(string[] args)
+    {
+        var values = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
+        for (var i = 0; i < args.Length; i++)
+        {
+            var arg = args[i];
+            if (!arg.StartsWith("--", StringComparison.Ordinal))
+            {
+                continue;
+            }
+
+            var body = arg[2..];
+            var eq = body.IndexOf('=', StringComparison.Ordinal);
+            if (eq >= 0)
+            {
+                values[body[..eq]] = body[(eq + 1)..];
+            }
+            else if (ValueOptions.Contains(body) && i + 1 < args.Length)
+            {
+                values[body] = args[++i];
+            }
+            else
+            {
+                values[body] = null;
+            }
+        }
+
+        values.TryGetValue("dataPath", out var dataPath);
+        values.TryGetValue("setconfig", out var setConfig);
+        values.TryGetValue("port", out var portText);
+        int? port = int.TryParse(portText, NumberStyles.None, CultureInfo.InvariantCulture, out var n) ? n : null;
+        return new CommandLine(dataPath, port, setConfig);
+    }
+}