Tests: Record dates by instant in the drop-in snapshot

* DropInSnapshot.j:
  - Describe a CPDate by its UTC instant instead of its class name.
  - Record the string value of a control holding a date by the date's instant, since the browser formats it in the local time zone.

* DropInArchives.json: Update the CPDatePicker entry to the instant it archives.

* DropInArchiveTest.j: State that the test must pass in every time zone, and how to check it in UTC.

Tests/AppKit/DropInArchiveTest.j

@@ -125,6 +125,14 @@ var fs = require("fs"),
 
 /*
     An archive written by main must restore the view it was written from.
+
+    The descriptions compared must be the same on every machine. A date, and the
+    string value of a control that holds one, are recorded by the date's instant in
+    UTC, because their text is in the local time zone (DropInSnapshot.j). GitHub's
+    continuous integration runs this test in UTC, so run it in UTC as well as in the
+    local time zone before committing a change:
+
+        TZ=UTC npx jake test
 */
 - (void)testExistingArchivesRestoreTheOriginalView
 {

Tests/AppKit/DropInSnapshot.j

@@ -165,6 +165,13 @@ function DropInDescribeValue(aValue)
 
     if (aValue.isa)
     {
+        /*
+         A date is recorded by its instant in UTC. Its description is in the time zone
+         of the machine that runs the test, so it differs between machines.
+         */
+        if ([aValue isKindOfClass:[CPDate class]])
+            return "CPDate:" + (isNaN(aValue.getTime()) ? "invalid" : aValue.toISOString());
+
         if ([aValue isKindOfClass:[CPColor class]])
             return "CPColor:" + [aValue cssString];
 
@@ -286,6 +293,15 @@ function DropInViewTreeState(aView)
 
         var value = [aView performSelector:selector];
 
+        /*
+         A control that holds a date gives its string value in the time zone of the
+         machine that runs the test, because the browser formats it, not Cappuccino. It
+         is recorded by the date's instant instead, so that every machine records the
+         same snapshot.
+         */
+        if (aGetter === @"stringValue" && [aView respondsToSelector:@selector(objectValue)] && [[aView objectValue] isKindOfClass:[CPDate class]])
+            value = [aView objectValue];
+
         state[aGetter] = DropInDescribeValue(DropInBooleanGetters.indexOf(aGetter) !== -1 ? !!value : value);
     });
 

Tests/AppKit/Resources/DropInArchives.json

@@ -755,8 +755,8 @@
     "lineBreakMode": "2",
     "verticalAlignment": "1",
     "doubleValue": "0",
-    "objectValue": "CPDate",
-    "stringValue": "Sat Oct 31 2026 06:00:00 GMT-0600 (Mountain Daylight Time)",
+    "objectValue": "CPDate:2026-10-31T12:00:00.000Z",
+    "stringValue": "CPDate:2026-10-31T12:00:00.000Z",
     "tag": "-1"
    },
    "subviews": [