1. The old `prepareQueryArg` did double-unescaping of form value.
2. By the way, remove the unnecessary `ctx.Flash = ...` in
`MockContext`.
Co-authored-by: Giteabot <teabot@gitea.io>
Just like `models/unittest`, the testing helper functions should be in a
separate package: `contexttest`
And complete the TODO:
> // TODO: move this function to other packages, because it depends on
"models" package