Generator tests: prevent parallel running tests

Author: greenrobot-team

.gitlab-ci.yml

@@ -84,7 +84,10 @@ generator-integ-tests:
     # Generator tests
     - cd generator
     - dart pub get
-    - dart test
+    # generator test suites must not run in parallel (see notes on GeneratorTestEnv):
+    # Set concurrency=1 to run only one test suite (== test file) at a time.
+    # Set --reporter expanded to print log for every completed test.
+    - dart test --concurrency=1 --reporter expanded
     # ObjectBox tests
     - cd ../objectbox_test
     - ../install.sh

generator/test/generator_test_env.dart

@@ -13,6 +13,13 @@ import 'package:test/test.dart';
 /// Helps testing the generator by running [EntityResolver] on the given
 /// [source] file and feeding the output directly into [CodeBuilder] and running
 /// it.
+///
+/// Warning: tests that use this or otherwise create files in the `lib` folder
+/// should not run in parallel as this might break when reading unexpected
+/// files from the `lib` folder (see [run] which calls
+/// `TestReaderWriter.testing.loadIsolateSources()`). So make sure tests are in
+/// the same test suite (`main()` method) and use `dart test --concurrency=1`.
+/// See also https://pub.dev/packages/test#test-concurrency.
 class GeneratorTestEnv {
   final EntityResolver resolver;
   final Config config;