errors: add test for Join
Change-Id: I77c61211a488c66f1d445c0bf01e35aaf4f83565
GitHub-Last-Rev:
c411a56a3b5215e6dd093be7069affb176b48dfd
GitHub-Pull-Request: golang/go#56279
Reviewed-on: https://go-review.googlesource.com/c/go/+/443316
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>