content test: Aim taps on links more precisely at the text

By saying `tester.tapAt(find.text('hello'))`, we had been aiming
at the center of the Text widgets, and expecting that to hit the
recognizer we've put on the span, even though the widget is much
wider than the span and the latter doesn't reach the former's center.
Effectively we were relying on the presence of issue #214.

But with an upstream change yesterday:
  flutter/flutter#140621
such a tap no longer hits the span.  That broke these tests.

To fix them, aim the taps near the start of the widget instead.

Fixes: #475

Author: gnprice

test/widgets/content_test.dart

@@ -62,6 +62,13 @@ void main() {
     });
   });
 
+  Future<void> tapText(WidgetTester tester, Finder textFinder) async {
+    final height = tester.getSize(textFinder).height;
+    final target = tester.getTopLeft(textFinder)
+      .translate(height/4, height/2); // aim for middle of first letter
+    await tester.tapAt(target);
+  }
+
   group('LinkNode interactions', () {
     // The Flutter test font uses square glyphs, so width equals height:
     //   https://github.com/flutter/flutter/wiki/Flutter-Test-Fonts
@@ -85,7 +92,7 @@ void main() {
       await prepareContent(tester,
         '<p><a href="https://example/">hello</a></p>');
 
-      await tester.tap(find.text('hello'));
+      await tapText(tester, find.text('hello'));
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: Uri.parse('https://example/'), mode: LaunchMode.platformDefault));
     }, variant: const TargetPlatformVariant({TargetPlatform.android, TargetPlatform.iOS}));
@@ -111,7 +118,7 @@ void main() {
     testWidgets('link nested in other spans', (tester) async {
       await prepareContent(tester,
         '<p><strong><em><a href="https://a/">word</a></em></strong></p>');
-      await tester.tap(find.text('word'));
+      await tapText(tester, find.text('word'));
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: Uri.parse('https://a/'), mode: LaunchMode.platformDefault));
     });
@@ -134,15 +141,15 @@ void main() {
     testWidgets('relative links are resolved', (tester) async {
       await prepareContent(tester,
         '<p><a href="/a/b?c#d">word</a></p>');
-      await tester.tap(find.text('word'));
+      await tapText(tester, find.text('word'));
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: Uri.parse('${eg.realmUrl}a/b?c#d'), mode: LaunchMode.platformDefault));
     });
 
     testWidgets('link inside HeadingNode', (tester) async {
       await prepareContent(tester,
         '<h6><a href="https://a/">word</a></h6>');
-      await tester.tap(find.text('word'));
+      await tapText(tester, find.text('word'));
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: Uri.parse('https://a/'), mode: LaunchMode.platformDefault));
     });
@@ -151,7 +158,7 @@ void main() {
       await prepareContent(tester,
         '<p><a href="file:///etc/bad">word</a></p>');
       testBinding.launchUrlResult = false;
-      await tester.tap(find.text('word'));
+      await tapText(tester, find.text('word'));
       await tester.pump();
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: Uri.parse('file:///etc/bad'), mode: LaunchMode.platformDefault));
@@ -187,7 +194,7 @@ void main() {
       final pushedRoutes = await prepareContent(tester,
         html: '<p><a href="/#narrow/stream/1-check">stream</a></p>');
 
-      await tester.tap(find.text('stream'));
+      await tapText(tester, find.text('stream'));
       check(testBinding.takeLaunchUrlCalls()).isEmpty();
       check(pushedRoutes).single.isA<WidgetRoute>()
         .page.isA<MessageListPage>().narrow.equals(const StreamNarrow(1));
@@ -198,7 +205,7 @@ void main() {
       final pushedRoutes = await prepareContent(tester,
         html: '<p><a href="/#narrow/stream/1-check/topic">invalid</a></p>');
 
-      await tester.tap(find.text('invalid'));
+      await tapText(tester, find.text('invalid'));
       final expectedUrl = eg.realmUrl.resolve('/#narrow/stream/1-check/topic');
       check(testBinding.takeLaunchUrlCalls())
         .single.equals((url: expectedUrl, mode: LaunchMode.platformDefault));