fix: improve AutoTestLintOffsets reliability

handles edge cases when there are multiple similar code fragments

Author: andrew-bekhiet-solid

test/lints/auto_test_lint_offsets.dart

@@ -1,23 +1,55 @@
 import 'package:analyzer_testing/analysis_rule/analysis_rule.dart';
+import 'package:analyzer_testing/src/analysis_rule/pub_package_resolution.dart';
+import 'package:collection/collection.dart';
 
 mixin AutoTestLintOffsets on AnalysisRuleTest {
-  List<String> _expectedCodeFragments = [];
+  int _nextPlaceholderId = 0;
+  final Map<String, String> _placeholderToCode = {};
 
   Future<void> assertAutoDiagnostics(String source) async {
     try {
-      final expectedDiagnostics = [
-        for (final codeFragment in _expectedCodeFragments)
-          lint(source.indexOf(codeFragment), codeFragment.length),
-      ];
+      final placeholders = _placeholderToCode.entries
+          .map(
+            (entry) => (
+              placeholder: entry.key,
+              code: entry.value,
+              index: source.indexOf(entry.key),
+            ),
+          )
+          .sorted((a, b) => a.index.compareTo(b.index));
 
-      await assertDiagnostics(source, expectedDiagnostics);
+      final expectedDiagnostics = <ExpectedDiagnostic>[];
+      int replacedPlaceholdersDelta = 0;
+
+      for (final match in placeholders) {
+        if (match.index == -1) {
+          throw StateError(
+            'Expected lint placeholder "${match.placeholder}" was not found in source.',
+          );
+        }
+
+        expectedDiagnostics.add(
+          lint(match.index + replacedPlaceholdersDelta, match.code.length),
+        );
+        replacedPlaceholdersDelta +=
+            match.code.length - match.placeholder.length;
+      }
+
+      final resolvedSource = _placeholderToCode.entries.fold(
+        source,
+        (resolved, entry) => resolved.replaceFirst(entry.key, entry.value),
+      );
+
+      await assertDiagnostics(resolvedSource, expectedDiagnostics);
     } finally {
-      _expectedCodeFragments = [];
+      _nextPlaceholderId = 0;
+      _placeholderToCode.clear();
     }
   }
 
   String expectLint(String code) {
-    _expectedCodeFragments.add(code);
-    return code;
+    final placeholder = '__AUTO_TEST_LINT_${_nextPlaceholderId++}__';
+    _placeholderToCode[placeholder] = code;
+    return placeholder;
   }
 }