tests/test-admin-commands.t

interfaces: introduce and use a protocol class for the `charencoding` module

See f2832de2a46c for details when this was done for the `bdiff` module.

This lets us dump the hack where the `pure` implementation was imported during
the type checking phase to provide signatures for the module methods it
provides.  Now the protocol classes are starting to shine, because these methods
are provided by `pure.charencoding` and `cext.parsers`, and references to
`cffi.charencoding` and `cext.charencoding` are forwarded to them as appropriate
by the `policy` module.  But none of that matters, as long as the module
returned provides the listed methods.

The interface was copy/pasted from the `pure` module, but `jsonescapeu8fallback`
is omitted because it is accessed from the `pure` module directly when the
escaping fails in the primary module's `jsonescapeu8()`.

Test admin::verify

  $ hg init admin-verify
  $ cd admin-verify

Test normal output

  $ hg admin::verify -c dirstate
  running 1 checks
  running working-copy.dirstate
  checking dirstate

Quiet works

  $ hg admin::verify -c dirstate --quiet

Test no check no options

  $ hg admin::verify
  abort: `checks` required
  [255]

Test single check without options

  $ hg admin::verify -c working-copy.dirstate
  running 1 checks
  running working-copy.dirstate
  checking dirstate

Test single check (alias) without options

  $ hg admin::verify -c dirstate
  running 1 checks
  running working-copy.dirstate
  checking dirstate

Test wrong check name without options

  $ hg admin::verify -c working-copy.dir
  abort: unknown check working-copy.dir
  (did you mean working-copy.dirstate?)
  [10]

Test wrong alias without options

  $ hg admin::verify -c dir
  abort: unknown check dir
  [10]