content [test]: Add golden tests for KaTeX content

Author: rajveermalviya

test/widgets/content_test.dart

@@ -1,10 +1,14 @@
 import 'package:checks/checks.dart';
+import 'package:file/file.dart';
+import 'package:file/local.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_checks/flutter_checks.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:path/path.dart' as p;
 import 'package:url_launcher/url_launcher.dart';
 import 'package:zulip/api/core.dart';
 import 'package:zulip/model/content.dart';
@@ -723,6 +727,43 @@ void main() {
         });
       }
     });
+
+    testWidgets('golden tests', (tester) async {
+      await _loadKatexFonts();
+
+      addTearDown(testBinding.reset);
+      final globalSettings = testBinding.globalStore.settings;
+      await globalSettings.setBool(BoolGlobalSetting.renderKatex, true);
+      check(globalSettings).getBool(BoolGlobalSetting.renderKatex).isTrue();
+
+      final contentHtml =
+          ContentExample.mathBlockKatexSizing.html +
+          ContentExample.mathBlockKatexNestedSizing.html +
+          ContentExample.mathBlockKatexDelimSizing.html +
+          ContentExample.mathBlockKatexVertical1.html +
+          ContentExample.mathBlockKatexVertical2.html +
+          ContentExample.mathBlockKatexVertical3.html +
+          ContentExample.mathBlockKatexVertical4.html +
+          ContentExample.mathBlockKatexVertical5.html;
+
+      await prepareContent(tester, Builder(builder: (context) =>
+        DefaultTextStyle(
+          style: ContentTheme.of(context).textStylePlainParagraph,
+          child: BlockContentList(
+            nodes: parseContent(contentHtml).nodes.map((node) {
+              final mathBlockNode = node as MathBlockNode;
+              return ParagraphNode(
+                links: null,
+                nodes: [
+                  MathInlineNode(
+                    texSource: mathBlockNode.texSource,
+                    nodes: mathBlockNode.nodes),
+                ]);
+            }).toList(growable: false)))));
+
+      await check(find.byType(BlockContentList))
+        .matchesGoldenFile(Uri.file('goldens/katex.png'));
+    });
   });
 
   /// Make a [TargetFontSizeFinder] to pass to [checkFontSizeRatio],
@@ -1469,3 +1510,21 @@ void main() {
     });
   });
 }
+
+Future<void> _loadKatexFonts() async {
+  const fs = LocalFileSystem();
+  final katexFontsDir = fs.currentDirectory.childDirectory(
+    fs.path.join('assets', 'KaTeX'));
+  assert(katexFontsDir.existsSync());
+
+  for (final fontFile in katexFontsDir.listSync()) {
+    if (fontFile is! File) continue;
+    if (p.extension(fontFile.path) != '.ttf') continue;
+
+    final [fontName, ...] = p.withoutExtension(fontFile.basename).split('-');
+
+    final bytes =
+      Future.value(fontFile.readAsBytesSync().buffer.asByteData());
+    await (FontLoader(fontName)..addFont(bytes)).load();
+  }
+}