Tests type_variable_bounds4_test.dart have too weak logic

[eernstg]

During Dart 2.0 test migration, it became evident that the test type_variable_bounds4_test.dart (which currently exists in language and language_strong and will soon exist in language_2) uses a multi-test logic which is too weak: It surely intends to check that about 10 different situations cause a compile-time error (a static type warning in Dart 1.x), but it will in fact succeed as long as any non-empty subset of them causes an error. In other words, we might fail to have 9 out of 10 expected errors, and nobody would notice. The test needs to use a different multi-test logic such that each error is checked separately.

Here's some code that has nothing to do with the actual test, but which shows the core of the issue:

main() {
  // Let's say we think this should be flagged as an error.
  int x = 42; //# 01: compile-time error

  // We also think this should be flagged as an error.
  x = x + 1; //# 01: continued

  // ... somewhere in the middle, we have a real error.
  by the way, here's a real error. //# 01: continued
}

The intention is that each line marked with //# 01: .. should be flagged as an error, but the effect is that this test succeeds because a non-empty subset of the marked lines actually contains an error. The following would work:

main() {
  // This declaration is expected to cause several usages to incur a compile-time error.
  int x = 42;
  x = x + 1; //# 01: compile-time error
  by the way, here's a real error. //# 02: compile-time error
}

We would then notice that there is no error for x = x + 1, as we should.

We have about 2558 occurrences of continued in test files under tests; it is not obvious whether this is a single exception or the issue may affect several tests.

[eernstg]

Note that test files containing multiple occurrences of /*@compile-error=unspecified*/ use the same (faulty) logic: If just one compile-time error occurs then the complete test run is considered successful, even though we may have just one actual compile-time error, and all the others are free-riders. As of Feb 2018, the following test files in tests/language_2 have this problem:

factory2_test.dart
factory3_test.dart
field1_test.dart
field_method4_test.dart
on_catch_malformed_type_test.dart
operator5_test.dart
operator_equals_test.dart
regress_12561_test.dart
regress_19728_test.dart
return_type_test.dart
type_inference_circularity_test.dart
type_variable_bounds2_test.dart