1 files changed, 77 insertions, 0 deletions
diff --git a/HutchTests/MailingListActivityTests.swift b/HutchTests/MailingListActivityTests.swift
new file mode 100644
index 0000000..46208cb
--- /dev/null
+++ b/HutchTests/MailingListActivityTests.swift
@@ -0,0 +1,77 @@
+import Foundation
+import Testing
+@testable import Hutch
+
+struct MailingListActivityTests {
+
+    @Test
+    func usesTheNewestArrivalOverTheRootTimestamp() {
+        // The case that started this: sr.ht reports thread.updated seven seconds
+        // after the root email on a thread carrying four replies, so the fallback
+        // must lose to real arrival data.
+        let rootInsert = Date(timeIntervalSince1970: 1_000)
+        let newestReply = Date(timeIntervalSince1970: 5_000)
+        let activity = MailingListActivity(newestByRootEmailID: [42: newestReply])
+
+        #expect(activity.lastActivity(rootEmailID: 42, fallback: rootInsert) == newestReply)
+    }
+
+    @Test
+    func fallsBackForThreadsOutsideTheScannedWindow() {
+        // Threads with nothing new are absent from the feed scan; they keep the
+        // root timestamp, which is older than any cutoff and so reads as read.
+        let rootInsert = Date(timeIntervalSince1970: 1_000)
+        let activity = MailingListActivity(newestByRootEmailID: [:])
+
+        #expect(activity.lastActivity(rootEmailID: 42, fallback: rootInsert) == rootInsert)
+    }
+
+    @Test
+    func neverGoesBackwardsFromTheFallback() {
+        // A root inserted after the newest scanned reply must not age the thread
+        // backwards.
+        let rootInsert = Date(timeIntervalSince1970: 9_000)
+        let staleReply = Date(timeIntervalSince1970: 5_000)
+        let activity = MailingListActivity(newestByRootEmailID: [42: staleReply])
+
+        #expect(activity.lastActivity(rootEmailID: 42, fallback: rootInsert) == rootInsert)
+    }
+
+    @Test
+    func tracksThreadsIndependently() {
+        let activity = MailingListActivity(newestByRootEmailID: [
+            1: Date(timeIntervalSince1970: 5_000),
+            2: Date(timeIntervalSince1970: 7_000)
+        ])
+        let fallback = Date(timeIntervalSince1970: 1_000)
+
+        #expect(activity.lastActivity(rootEmailID: 1, fallback: fallback) == Date(timeIntervalSince1970: 5_000))
+        #expect(activity.lastActivity(rootEmailID: 2, fallback: fallback) == Date(timeIntervalSince1970: 7_000))
+        #expect(activity.lastActivity(rootEmailID: 3, fallback: fallback) == fallback)
+    }
+
+    @Test
+    func newMailInAnOldThreadReadsAsUnread() {
+        let suiteName = "MailingListActivityTests-\(UUID().uuidString)"
+        let defaults = UserDefaults(suiteName: suiteName)!
+        defer { defaults.removePersistentDomain(forName: suiteName) }
+
+        let signIn = Date(timeIntervalSince1970: 5_000)
+        InboxReadStateStore.establishBaselineIfNeeded(now: signIn, defaults: defaults)
+
+        // A thread rooted long before sign-in, with a reply after it. Keyed on
+        // thread.updated this reads as read, which was the bug.
+        let rootInsert = Date(timeIntervalSince1970: 1_000)
+        let replyAfterSignIn = Date(timeIntervalSince1970: 6_000)
+        let activity = MailingListActivity(newestByRootEmailID: [42: replyAfterSignIn])
+        let lastActivityAt = activity.lastActivity(rootEmailID: 42, fallback: rootInsert)
+
+        #expect(
+            InboxReadStateStore.isUnread(
+                threadID: "list#old thread",
+                lastActivityAt: lastActivityAt,
+                defaults: defaults
+            )
+        )
+    }
+}