Add CodeGenerator tests and fix NREs/bugs

[hughbe]

Depends on #39585

[danmoseley]

@buyaa-n your area, could you please help get this in

[krwq]

product changes LGTM (with one comment)

@hughbe does this need rebase on top of that PR? Presumably some changes will disappear

[buyaa-n]

Thank you @hughbe there is some test failures System.CodeDom.Tests Total: 3174, Errors: 0, Failed: 61, Skipped: 0, Time: 4. could take a look, excpet test failures looks great 👍. https://helix.dot.net/api/2019-06-17/jobs/8bd796a7-24f0-43b2-9566-be1cf5947d97/workitems/System.CodeDom.Tests/console

[maryamariyan]

Thanks for your PR @hughbe
Just checking if this is still under your radar and if you'll want to update it soon?
Assigned to you so it's easier for you to track.

[stephentoub]

Thanks, @hughbe.

I'm fine with the ArgumentNullException changes and the associated tests, but I think the changes that guard calls based on whether collections are empty should be reverted.

[buyaa-n]

I'm fine with the ArgumentNullException changes and the associated tests, but I think the changes that guard calls based on whether collections are empty should be reverted.

@hughbe if you have no time to apply the requested changes in near future please let me know, I can help wiith that. Thank you!

[danmoseley]

@buyaa-n I suggest just making the changes so we can get this one merged...

[buyaa-n]

@buyaa-n I suggest just making the changes so we can get this one merged...

Sure

[buyaa-n]

/azp run corefx-ci

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[buyaa-n]

I'm fine with the ArgumentNullException changes and the associated tests, but I think the changes that guard calls based on whether collections are empty should be reverted

@stephentoub reverted collection count checks, do you have any other comment?

[maryamariyan]

Thank you for your contribution. As announced in dotnet/coreclr#27549 this repository will be moving to dotnet/runtime on November 13. If you would like to continue working on this PR after this date, the easiest way to move the change to dotnet/runtime is:

1. In your corefx repository clone, create patch by running git format-patch origin
2. In your runtime repository clone, apply the patch by running git apply --directory src/corefx <path to the patch created in step 1>

[hughbe]

So sorry! I keep getting distracted by winforms stuff and university work. Thanks for taking this on.

[buyaa-n]

So sorry! I keep getting distracted by winforms stuff and university work. Thanks for taking this on.

Sure no problem, thank you for your contribution

[krwq]

Product changes and small tests file LGTM, haven't got time to look at the big tests change

[stephentoub]

Suggested change

	}
	}

[stephentoub]

Suggested change

	GenerateNamespaceImport(imp);
	GenerateNamespaceImport(imp);