add some tests

[xcaptain]

Still work in progress, test cases are copied from Casbin.NET project, in the future more tests should be added.

[hsluoyz]

Please fix.

[xcaptain]

@hsluoyz do you think we should implement all the test cases from Casbin.NET or just some? also how about we move this project into Casbin.NET because this project is so simple and share a lot of tests with Casbin.NET

[hsluoyz]

If your adapter supports AutoSave, then you should follow: https://github.com/casbin/xorm-adapter/blob/master/adapter_test.go. If not, then follow: https://github.com/casbin/cassandra-adapter/blob/master/adapter_test.go

I don't think moving into Casbin is a good idea. Because all adapters have their own repo.

And for the commits in this PR, please merge them into one single commit, for easier review.

[xcaptain]

@hsluoyz I think this adapter is using autosave and I can't think of any reason to disable autosave. By default DbContext in an asp dotnet core project is injected at scoped service, this adapter depends on DbContext, so its lifetime must be scoped or transient, which means this adapter will be created per requests, which means write or read from database per request.

Thanks for pointing out how to test an adapter, I will follow your xorm-adapter project.

[xcaptain]

@hsluoyz Please take a look, I follow testAutoSave in xorm-adapter, the test cases passed in my laptop. I will rebase these commits before merge.

[hsluoyz]

lgtm. Please squash the commits.

[xcaptain]

rebased

[hsluoyz]

Merged.

[hsluoyz]

Hi @xcaptain , next step, please add the CI and code coverage badges.