Flutter update breaks link interaction tests

[gnprice]

After a Flutter update, some tests are failing in main. This is visible also in the recent PRs #472 and #474, as here:
https://github.com/zulip/zulip-flutter/actions/runs/7391944552/job/20109637276?pr=472

The failure looks like this:

$ flutter test test/widgets/content_test.dart --name 'can tap a link'
00:02 +0: LinkNode interactions can tap a link to open URL (variant: TargetPlatform.android)
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure was thrown running a test:
Expected: a List<({LaunchMode mode, Uri url})> that:
  has single element
Actual: []
Which: has no elements

When the exception was thrown, this was the stack:
#0      check.<anonymous closure> (package:checks/src/checks.dart:72:9)
#1      _TestContext.nest (package:checks/src/checks.dart:760:12)
#2      IterableChecks.single (package:checks/src/extensions/iterable.dart:33:36)
#3      main.<anonymous closure>.<anonymous closure> (file:///home/greg/z/flutterz/test/widgets/content_test.dart:90:10)
<asynchronous suspension>
#4      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:168:15)
<asynchronous suspension>
#5      TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:1017:5)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

The test description was:
  can tap a link to open URL (variant: TargetPlatform.android)
════════════════════════════════════════════════════════════════════════════════════════════════════
00:02 +0 -1: LinkNode interactions can tap a link to open URL (variant: TargetPlatform.android) [E]
  Test failed. See exception logs above.
  The test description was: can tap a link to open URL (variant: TargetPlatform.android)
  

To run this test again: /home/greg/n/flutter/flutter/bin/cache/dart-sdk/bin/dart test /home/greg/z/flutterz/test/widgets/content_test.dart -p vm --plain-name 'LinkNode interactions can tap a link to open URL (variant: TargetPlatform.android)'

The test renders some content that has a link in it, then taps the link and checks that the tap made it to the binding for launchUrl. The check fails — apparently the tap didn't make it to the binding.

On the other hand, following a link in the actual app seems to work fine. So this may only affect the tests.

More investigation needed.

[gnprice]

OK, here's the upstream change that caused this breakage:

• Reland "Make TextSpan hit testing precise." (#140468) flutter/flutter#140621

So chalk up another one for #239, then.

The change sounds like a good one. Still investigating to determine why it breaks the tests and what the right fix is.

[gnprice]

OK, the core of the issue is that we say things like this:

    testWidgets('can tap a link to open URL', (tester) async {
      await prepareContent(tester,
        '<p><a href="https://example/">hello</a></p>');
      await tester.tapAt(find.text('hello'));

and tapAt means tapping at the center of the widget. So we're tapping at the center of a Text widget; but the widget extends the full width, and the actual glyphs laid out as the paragraph inside it only occupy the start of that, without reaching the center.

There's a few possible ways we might fix that: possibly the Text widget we build for a ParagraphNode of Zulip content should only go as wide as its internal layout, or possibly the tests should just change where they tap.