Guanqun add unit tests

[gavofyork]

No description provided.

[gavofyork]

not building properly. @General-Beck ?

[guanqun]

I used cargo test -p ethjson and it worked fine locally. What's the issue? I see "All checks have passed" from CI.

[rphmeier]

@guanqun https://gitlab.parity.io/parity/parity/builds/54720 indicates that the build was skipped because it modified no Rust files, which definitely isn't true. I'll try retrying

[guanqun]

aha, I think I know the problem, here's the fix for it. 14b715b

The original script only detects for "^js", interesting enough, I'm modifying "json"...

But I don't have permission to push to guanqun-add-unit-tests, probably someone can cherry-pick this commit.

[arkpar]

This is really great, thanks a lot!