Implemented phase 3 for the POC prototype in the Website service.

Services/Website/Tests/Library/Cases/Internal/Extensions/DateStampsTests.swift

@@ -0,0 +1,45 @@
+import Foundation
+import Testing
+
+@testable import WebsiteLibrary
+
+@Suite(
+    "Date+Stamps extension",
+    .tags(.extensionTests)
+)
+struct DateStampsTests {
+
+    // MARK: Methods tests
+
+    @Test(arguments: zip(
+        [0, -86_400, -172_800, -25_920_000] as [TimeInterval],
+        ["today, 09:14", "yesterday, 09:14", "21 Sep, 09:14", "27 Nov 2025, 08:14"]
+    ))
+    func `stamps a date relative to today, on Amsterdam's clock`(
+        offset: TimeInterval,
+        expects stamp: String
+    ) {
+        #expect(Date.stub.addingTimeInterval(offset).stamp(relativeTo: .stub) == stamp)
+    }
+
+    @Test
+    func `tells days apart at Amsterdam's midnight, not UTC's`() {
+        // 23:30 and 01:00 in Amsterdam are 21:30 and 23:00 UTC: one day to UTC, two to Amsterdam.
+        let lateEvening = Date.stub.addingTimeInterval(-35_040)
+        let smallHours = Date.stub.addingTimeInterval(-29_640)
+
+        #expect(lateEvening.stamp(relativeTo: smallHours) == "yesterday, 23:30")
+    }
+
+    @Test(arguments: zip(
+        [171_000, 1_800, 180_000, 259_260] as [TimeInterval],
+        ["47 h left", "under an hour left", "2 days left", "3 days left"]
+    ))
+    func `counts down in hours, then days`(
+        interval: TimeInterval,
+        expects countdown: String
+    ) {
+        #expect(Date.stub.addingTimeInterval(interval).countdown(from: .stub) == countdown)
+    }
+
+}