Reimplement basic golden testing

Author: parlough

pubspec.yaml

@@ -12,5 +12,7 @@ dependencies:
   meta: ^1.16.0
 
 dev_dependencies:
+  collection: ^1.19.1
   night_raven_insight: ^4.0.0
+  path: ^1.9.1
   test: ^1.26.3

test/golden_test.dart

@@ -0,0 +1,84 @@
+/// End-to-end golden testing for `package:opal`.
+///
+/// ## Overview
+///
+/// Golden tests verify that language tokenization produces consistent,
+/// correct output by comparing against pre-generated reference files.
+///
+/// ## Testing structure
+///
+/// Tests are organized by language in `test/goldens/<language>/`:
+///
+/// - `.in` files contain input source code to tokenize.
+/// - `.out` files contain expected tokenization output.
+///
+/// Tests are automatically discovered based on the directory structure.
+/// Each language directory becomes a test group and
+/// each `.in` file becomes a test case.
+///
+/// ## Running tests
+///
+/// Run all golden tests:
+///
+/// ```bash
+/// dart test test/golden_test.dart
+/// ```
+///
+/// Run tests for a specific language:
+///
+/// ```bash
+/// dart test test/golden_test.dart --plain-name "dart"
+/// ```
+///
+/// ## Generating golden files
+///
+/// To create or update golden files:
+///
+/// 1. Create/edit the `.in` file in `test/goldens/<language>/`.
+/// 2. Set [generateGoldens] to `true` in this file.
+/// 3. Run: `dart test test/golden_test.dart`.
+/// 4. Review the generated `.out` files.
+/// 5. Set [generateGoldens] back to `false`.
+///
+/// The generator automatically discovers all `.in` files and
+/// generates the corresponding `.out` files.
+library;
+
+import 'package:test/test.dart';
+
+import 'goldens/golden_test_util.dart';
+
+/// Set to `true` to generate golden files instead of running tests.
+const generateGoldens = false;
+
+void main() {
+  // Discover all languages and their test cases from the file system.
+  final suite = GoldenTestSuite.discover();
+
+  if (generateGoldens) {
+    // Create or update all golden files.
+    group('Generate golden files', () {
+      test('generate all', () async {
+        for (final language in suite.languages) {
+          for (final goldenTest in language.tests) {
+            await goldenTest.generate(suite.registry);
+            print('Generated: ${language.name}/${goldenTest.name}.out');
+          }
+        }
+      });
+    });
+
+    return;
+  }
+
+  // Run all discovered golden tests.
+  for (final language in suite.languages) {
+    group(language.name, () {
+      for (final goldenTest in language.tests) {
+        test(goldenTest.name, () async {
+          await goldenTest.run(suite.registry);
+        });
+      }
+    });
+  }
+}

test/goldens/dart/hello-world.in

@@ -0,0 +1,6 @@
+const String message = 'Hello, world!';
+
+void main() {
+  // Print the message.
+  print('The message is: $message');
+}

test/goldens/dart/hello-world.out

@@ -0,0 +1,68 @@
+const String message = 'Hello, world!';
+^^^^^
+source-code-dart-keyword-const
+     ^
+     source-code-dart-whitespace
+      ^^^^^^
+      source-code-dart-identifier-type-built-in
+            ^
+            source-code-dart-whitespace
+             ^^^^^^^
+             source-code-dart-identifier
+                    ^
+                    source-code-dart-whitespace
+                     ^
+                     source-code-dart-keyword-operator
+                      ^
+                      source-code-dart-whitespace
+                       ^
+                       source-code-dart-literal-string-literal-string-begin
+                        ^^^^^^^^^^^^^
+                        source-code-dart-literal-string-literal-string-unquoted
+                                     ^
+                                     source-code-dart-literal-string-literal-string-end
+                                      ^
+                                      source-code-dart-punctuation
+
+void main() {
+^^^^
+source-code-dart-identifier-type-built-in
+    ^
+    source-code-dart-whitespace
+     ^^^^
+     source-code-dart-identifier-function
+         ^
+         source-code-dart-punctuation
+          ^
+          source-code-dart-punctuation
+           ^
+           source-code-dart-whitespace
+            ^
+            source-code-dart-punctuation
+  // Print the message.
+^^
+source-code-dart-whitespace
+  ^^^^^^^^^^^^^^^^^^^^^
+  source-code-dart-comment-line
+  print('The message is: $message');
+^^
+source-code-dart-whitespace
+  ^^^^^
+  source-code-dart-identifier-function
+       ^
+       source-code-dart-punctuation
+        ^
+        source-code-dart-literal-string-literal-string-begin
+         ^^^^^^^^^^^^^^^^
+         source-code-dart-literal-string-literal-string-unquoted
+                         ^^^^^^^^
+                         source-code-dart-literal-string-literal-string-unquoted-literal-string-interpolation
+                                 ^
+                                 source-code-dart-literal-string-literal-string-end
+                                  ^
+                                  source-code-dart-punctuation
+                                   ^
+                                   source-code-dart-punctuation
+}
+^
+source-code-dart-punctuation