Improve Encoding Fallback Tests (34.9%, 6.2%)

[benaadams]

Tracking issue

Encoding Fallback issue was detected via CI failure in XML tests rather than via Encoding tests

see: dotnet/corefx#16252 (comment)

/cc @danmosemsft

[benaadams]

Code coverage for
DecoderFallbackBufferHelper 29.8% (16.6% branch)
EncoderFallbackBufferHelper 34.9% (6.2% branch)

[tarekgh]

@benaadams are you willing to help with this one too?

[benaadams]

Encoding has burnt me twice; might have to lick my wounds for a little while... Though I do still want it to be faster; but may be a little while.

[benaadams]

3rd time I'd have to get it perfect 😉

[tarekgh]

when you look at it again we need to consider pick up the optimization from the corefxlab with it. also I am wondering why you didn't see Xml failure in your tests? didn't these tests run in your case?

[benaadams]

I normally end up with quite a few test failures in unrelated areas (without any changes) and testing coreclr against corefx can be periodically hit and miss as things change.

So I confirm the copy dlls works with current (at least in area); add a definite mistake (in area) to confirm that changes are picked up and failure happens; then test against new changes and ensure everything passes.

Probably should start raising issues for "unrelated" test failures I see and pay more attention to them...

[benaadams]

Be nice if there was an automated dotnetbot confirm with corefx in coreclr https://github.com/dotnet/coreclr/issues/9715

[danmoseley]

Info on code coverage work:

1. Here's the all up report
   https://ci.dot.net/job/dotnet_corefx/job/master/job/code_coverage_windows/Code_Coverage_Report/
   Caveat - doesn't show coverage of any types whose implementation is in corelib (eg String, etc). If you want to look at that for now you must gather manually using instructions below.

2. Docs on code coverage work are here
   https://github.com/dotnet/corefx/blob/master/Documentation/building/code-coverage.md
   and some in
   https://github.com/dotnet/corefx/blob/master/Documentation/project-docs/developer-guide.md

3. There's innumerable places to add coverage -- we would love to focus on the most heavily used types and the least covered types to get the most benefit.

[benaadams]

The fallback handling is pretty weird and could be cleaned up a lot; however I don't have a 100% handle on what its doing (clearly 😛 )

[GrabYourPitchforks]

@layomia Can we get new numbers for the current state of 5.0 master? Is this work already largely done?