Currently RSpec 2 is used but this is really not ideal as it is very easy to accidentally override some RSpec methods by require-ing the full mspec. It's also confusing as both frameworks use mostly the same methods.

Tests for mspec itself should be written in a very simple test harness like minitest, or for instance mruby's assert.rb, so that newer implementations can easily run them.

The current tests are heavily relying on mocks, so that might be non-trivial to replace.
In general I'm in favor of removing these white-box mock tests and instead test at a higher level for the functionality and not for a specific implementation.