Fix image source matcher tests so they actually run correctly

Author: Sub6Resources

packages/flutter_html_svg/test/svg_image_matcher_source_matcher_test.dart

@@ -0,0 +1,110 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_html/flutter_html.dart';
+import 'package:flutter_html_svg/flutter_html_svg.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:meta/meta.dart';
+
+void main() {
+  group("custom image data uri matcher", () {
+    CustomRenderMatcher matcher = svgDataUriMatcher(encoding: null, mime: 'image/svg+xml');
+    testImgSrcMatcher(
+      "matches an svg data uri with base64 encoding",
+      matcher,
+      imgSrc:
+      'data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4KPHN2ZyB2aWV3Qm94PSIwIDAgMzAgMjAiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyI+CjxjaXJjbGUgY3g9IjE1IiBjeT0iMTAiIHI9IjEwIiBmaWxsPSJncmVlbiIvPgo8L3N2Zz4=',
+      shouldMatch: true,
+    );
+    testImgSrcMatcher(
+      "matches an svg data uri without specified encoding",
+      matcher,
+      imgSrc:
+      'data:image/svg+xml,%3C?xml version="1.0" encoding="UTF-8"?%3E%3Csvg viewBox="0 0 30 20" xmlns="http://www.w3.org/2000/svg"%3E%3Ccircle cx="15" cy="10" r="10" fill="green"/%3E%3C/svg%3E',
+      shouldMatch: true,
+    );
+    testImgSrcMatcher(
+      "matches base64 data uri without data",
+      matcher,
+      imgSrc: 'data:image/svg+xml;base64,',
+      shouldMatch: true,
+    );
+    testImgSrcMatcher(
+      "doesn't match non-base64 image data uri",
+      matcher,
+      imgSrc:
+      'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==',
+      shouldMatch: false,
+    );
+    testImgSrcMatcher(
+      "doesn't match different mime data uri",
+      matcher,
+      imgSrc: 'data:text/plain;base64,',
+      shouldMatch: false,
+    );
+    testImgSrcMatcher(
+      "doesn't non-data schema",
+      matcher,
+      imgSrc: 'http:',
+      shouldMatch: false,
+    );
+    testImgSrcMatcher(
+      "doesn't match null",
+      matcher,
+      imgSrc: null,
+      shouldMatch: false,
+    );
+    testImgSrcMatcher(
+      "doesn't match empty",
+      matcher,
+      imgSrc: '',
+      shouldMatch: false,
+    );
+  });
+}
+
+String _fakeElement(String? src) {
+  return """
+      <img src="$src" />
+    """;
+}
+
+@isTest
+void testImgSrcMatcher(
+    String name,
+    CustomRenderMatcher matcher, {
+      required String? imgSrc,
+      required bool shouldMatch,
+    }) {
+  testWidgets(name, (WidgetTester tester) async {
+    await tester.pumpWidget(
+      TestApp(
+        Html(
+          data: _fakeElement(imgSrc),
+          customRenders: {
+            matcher: CustomRender.widget(
+              widget: (RenderContext context, _) {
+                return Text("Success");
+              },
+            ),
+          },
+        ),
+      ),
+    );
+    await expectLater(find.text("Success"), shouldMatch ? findsOneWidget : findsNothing);
+  });
+}
+
+class TestApp extends StatelessWidget {
+  final Widget body;
+
+  TestApp(this.body);
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        body: body,
+        appBar: AppBar(title: Text('flutter_html')),
+      ),
+    );
+  }
+}