test(rules): verify failed save preserves committed owner settings

JobTrackerApi.Tests/RuleSettingsFreshnessTests.cs

@@ -8,6 +8,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Data.Sqlite;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
 using Moq;
 using Xunit;
 
@@ -15,6 +16,43 @@ namespace JobTrackerApi.Tests;
 
 public sealed class RuleSettingsFreshnessTests
 {
+    [Fact]
+    public async Task Failed_owner_save_preserves_committed_rules_and_a_later_success_refreshes_existing_readers()
+    {
+        await using var fixture = await Fixture.CreateAsync();
+        await using var readA = fixture.Context("owner-a");
+        await using var readB = fixture.Context("owner-b");
+        var ownerA = fixture.Controller(readA);
+        var ownerB = fixture.Controller(readB);
+        Assert.False(await FollowUp(ownerA, fixture.JobA, "list"));
+        Assert.False(await FollowUp(ownerB, fixture.JobB, "list"));
+
+        var failure = new SaveFailureInterceptor();
+        await using var write = fixture.Context("owner-a", failure);
+        await Assert.ThrowsAsync<DbUpdateException>(() => new RulesController(write).Update(Settings(1), default));
+        Assert.Equal(1, write.UserRuleSettings.Local.Single().AppliedFollowUpDays);
+        Assert.Equal(30, (await RulesEngine.GetSettings(write, default)).AppliedFollowUpDays);
+        Assert.False(await FollowUp(ownerA, fixture.JobA, "list"));
+        Assert.False(await FollowUp(ownerB, fixture.JobB, "list"));
+
+        failure.RejectWrites = false;
+        Assert.IsType<NoContentResult>(await new RulesController(write).Update(Settings(1), default));
+        Assert.True(await FollowUp(ownerA, fixture.JobA, "list"));
+        Assert.False(await FollowUp(ownerB, fixture.JobB, "list"));
+    }
+
+    private sealed class SaveFailureInterceptor : SaveChangesInterceptor
+    {
+        public bool RejectWrites { get; set; } = true;
+
+        public override ValueTask<InterceptionResult<int>> SavingChangesAsync(
+            DbContextEventData eventData, InterceptionResult<int> result, CancellationToken cancellationToken = default)
+        {
+            if (RejectWrites) throw new DbUpdateException("Synthetic settings storage failure");
+            return base.SavingChangesAsync(eventData, result, cancellationToken);
+        }
+    }
+
     [Theory]
     [InlineData("list")]
     [InlineData("board")]
@@ -158,11 +196,13 @@ public sealed class RuleSettingsFreshnessTests
         public int JobA { get; private set; }
         public int JobB { get; private set; }
 
-        public JobTrackerContext Context(string? owner)
+        public JobTrackerContext Context(string? owner, IInterceptor? interceptor = null)
         {
             var user = new Mock<ICurrentUserService>();
             user.SetupGet(x => x.UserId).Returns(owner);
-            return new JobTrackerContext(new DbContextOptionsBuilder<JobTrackerContext>().UseSqlite(_connection).Options, user.Object);
+            var options = new DbContextOptionsBuilder<JobTrackerContext>().UseSqlite(_connection);
+            if (interceptor is not null) options.AddInterceptors(interceptor);
+            return new JobTrackerContext(options.Options, user.Object);
         }
 
         public JobApplicationsController Controller(JobTrackerContext db) =>