DodoSSH/tests/DodoSSH.Client.App.Tests/ProbedDeviceKeyStoreTests.cs

using DodoSSH.Client.App.Platform;
using DodoSSH.Client.Session;
using NSubstitute;

namespace DodoSSH.Client.App.Tests;

/// <summary>
/// That the slow probe choosing a device key store runs once, and not on the thread that asked.
/// </summary>
/// <remarks>
/// On Windows the probe creates and deletes a TPM key, and it used to run synchronously on the UI thread at
/// startup and again after every unlock. See <see cref="ProbedDeviceKeyStore"/>.
/// </remarks>
public sealed class ProbedDeviceKeyStoreTests
{
    private static CancellationToken Token => TestContext.Current.CancellationToken;

    /// <remarks>
    /// "Off the caller's thread" is proved by blocking, not by comparing thread ids. The probe waits for a
    /// release the test only gives once construction has returned, so a probe run on the thread that
    /// constructed the store could never be released and times out instead. Thread ids proved nothing: the
    /// test itself runs on a pool thread, and that same thread is free to pick up the queued probe the
    /// moment the test awaits, which is what failed on CI with the code doing exactly the right thing.
    /// </remarks>
    [Fact]
    public async Task TheChoiceIsMadeOnce_OffTheCallersThread()
    {
        var probes = 0;
        var releasedInTime = false;

        using var release = new ManualResetEventSlim();
        var inner = Substitute.For<IDeviceKeyStore>();

        var store = new ProbedDeviceKeyStore(() =>
        {
            Interlocked.Increment(ref probes);
            releasedInTime = release.Wait(TimeSpan.FromSeconds(10));
            return inner;
        });

        var available = store.IsAvailableAsync(Token);
        available.IsCompleted.ShouldBeFalse("nothing has released the probe yet");
        release.Set();

        (await available).ShouldBeTrue();
        (await store.IsAvailableAsync(Token)).ShouldBeTrue();
        await store.TryLoadAsync(Token);

        releasedInTime.ShouldBeTrue("the probe ran on the thread that asked, so nothing could release it");
        probes.ShouldBe(1);

        // Availability is the choice, not a second probe through the store it chose.
        await inner.DidNotReceive().IsAvailableAsync(Arg.Any<CancellationToken>());
        await inner.Received(1).TryLoadAsync(Arg.Any<CancellationToken>());
    }

    [Fact]
    public async Task AMachineWithNoStore_IsUnavailable_AndForgettingIsHarmless()
    {
        var store = new ProbedDeviceKeyStore(static () => new UnavailableDeviceKeyStore());

        (await store.IsAvailableAsync(Token)).ShouldBeFalse();
        (await store.TryLoadAsync(Token)).ShouldBeNull();

        await store.ForgetAsync(Token);
    }
}