Serve static maintenance page with 503 when PocketBase is unreachable

Elternbeirat.Web.Tests/PocketBaseHealthCacheTests.cs

@@ -0,0 +1,73 @@
+using Elternbeirat.Web.Shared;
+
+namespace Elternbeirat.Web.Tests;
+
+/// <summary>
+/// Unit tests for the health cache behind the maintenance gate. The probe is a fake
+/// that counts its calls, so no PocketBase is needed.
+/// </summary>
+public class PocketBaseHealthCacheTests
+{
+    private readonly SteppingClock _clock = new(new DateTimeOffset(2026, 10, 1, 10, 0, 0, TimeSpan.Zero));
+    private int _probes;
+
+    private Func<CancellationToken, Task<bool>> Probe(bool healthy) =>
+        _ =>
+        {
+            _probes++;
+            return Task.FromResult(healthy);
+        };
+
+    [Fact]
+    public async Task Result_is_reused_within_the_lifetime()
+    {
+        var cache = new PocketBaseHealthCache(_clock);
+
+        await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);
+        _clock.Now += PocketBaseHealthCache.Lifetime - TimeSpan.FromSeconds(1);
+        var healthy = await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);
+
+        healthy.ShouldBeTrue();
+        _probes.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Stale_result_is_probed_again()
+    {
+        // The way back after an outage: once the lifetime is over, the new answer
+        // replaces the old one.
+        var cache = new PocketBaseHealthCache(_clock);
+
+        await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);
+        _clock.Now += PocketBaseHealthCache.Lifetime;
+        var healthy = await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);
+
+        healthy.ShouldBeTrue();
+        _probes.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Unhealthy_result_is_cached_too()
+    {
+        // While PocketBase is down, not every request should wait for a failing probe.
+        var cache = new PocketBaseHealthCache(_clock);
+
+        await cache.IsHealthyAsync(Probe(healthy: false), CancellationToken.None);
+        var healthy = await cache.IsHealthyAsync(Probe(healthy: true), CancellationToken.None);
+
+        healthy.ShouldBeFalse();
+        _probes.ShouldBe(1);
+    }
+
+    /// <summary>
+    /// A clock the test moves forward by hand, to step past the cache lifetime without
+    /// waiting.
+    /// </summary>
+    /// <param name="start">The moment the clock shows at first.</param>
+    private sealed class SteppingClock(DateTimeOffset start) : TimeProvider
+    {
+        public DateTimeOffset Now { get; set; } = start;
+
+        public override DateTimeOffset GetUtcNow() => Now;
+    }
+}