#2906. Add digit separators tests

[sgrekhov]

No description provided.

[eernstg]

Looks good!

I think it would make sense to double check that a particular situation isn't a syntax error, it's just a failed lookup (2._718 fails because int doesn't have a member named _718). I wrote a comment about this.

I looked at LanguageFeatures/Digit_separators/digit_separators_A04_t06.dart, thinking that there could be a similar situation there. I don't think so, after all, but the situation isn't quite clear. I wrote a comment on that, too.

[sgrekhov]

Thank you. Added new test to check the extension and comments regarding digit_separators_A04_t06.dart.
Also the directory renamed from Digin_separators to Digit-separators to follow naming stayle in Language-features. PTAL.

[eernstg]

LGTM

[eernstg]

Just one more thing: Shouldn't we use a flag in order to enable this feature (it's enabled by default in 3.6.0, but a bleeding edge build is on 3.6.0-edge which would be a lower version number than 3.6.0).

[sgrekhov]

Asked if we need it in the chat. The tests work on the bleeding edge without the flag.

sgrekhov@SGREKHOV-HP:~/Google/dart-sdk/sdk$ python3 tools/test.py -n cfe-strong-linux co19/LanguageFeatures/Digit-separators/
No build targets found.
Test configuration:
    cfe-strong-linux(architecture: x64, compiler: fasta, mode: release, runtime: none, system: linux)
Suites tested: co19
[00:48 | 100% | +   16 | -    0]

=== All 16 tests passed ===
sgrekhov@SGREKHOV-HP:~/Google/dart-sdk/sdk$ python3 tools/test.py -n analyzer-asserts-linux co19/LanguageFeatures/Digit-separators/
No build targets found.
Test configuration:
    analyzer-asserts-linux(architecture: x64, compiler: dart2analyzer, mode: release, runtime: none, system: linux, enable-asserts, use-sdk)
Suites tested: co19
[00:07 | 100% | +   16 | -    0]

=== All 16 tests passed ===

[eernstg]

LGTM