TestErrorIs/TestNotErrorIs: check error message contents

[craig65535]

This extends the TestErrorIs/TestNotErrorIs tests to check not only the result, but the error message that is logged.

@dolmen requested that I split this out from #1345, which improves the error message returned by ErrorAs.

[craig65535]

@dolmen Is there more that needs to be done on this PR?

[craig65535]

@dolmen Should I just close this, and either start fresh or give up? I don't understand what the hold up is here as I've done everything you asked.

For context, this started as a simple change 8 months ago to make the misleading assert.ErrorAs failure messages more useful. That isn't even in this PR; this one is just the test changes you requested to enable adding tests to the actual ErrorAs PR.

I need to know what kind of change is acceptable to you to improve assert.ErrorAs. I think we can both agree that that is at least a useful and attainable goal, and that leaves the question of how to make it happen.

[dolmen]

@craig65535 The hold up is that there are currently 152 waiting pull requests, I'm the only active maintainer and I'm not even allowed to merge my own PRs. I also have a day job and 4 kids.

[dolmen]

For improved readability, split the line:

Suggested change

	resultErrMsg: "Target error should not be in err chain:\n" +
	resultErrMsg: ""+
	"Target error should not be in err chain:\n" +

[craig65535]

The hold up is that there are currently 152 waiting pull requests, I'm the only active maintainer and I'm not even allowed to merge my own PRs. I also have a day job and 4 kids.

@dolmen I understand and I do appreciate the time you put into this project. But at the same time I can see a pattern where I think I've addressed everything, and then a few weeks later find out there's one more small change to make, and rinse and repeat.

I made the readability change you suggested. PTAL

[dolmen]

@craig65535 Could you review my own PRs, in hope one other co-maintainer might see them?

Just be aware that as a non-maintainer you are privileged: you just need me to approve and merge. While myself I need another maintainer to approve my MRs, but nobody else is active.