Add comprehensive tests for all RSpec matchers

Tests cover all matchers in the adapter:
- all, be, be_a/be_an, be_a_kind_of/be_kind_of
- be_an_instance_of/be_instance_of, be_between
- be_falsey/be_falsy, be_nil, be_truthy, be_within
- change, contain_exactly, cover, end_with
- eq, eql, equal, exist, have_attributes
- include, match, match_array, output
- raise_error/raise_exception, respond_to, satisfy
- start_with, throw_symbol
- yield_control, yield_successive_args
- yield_with_args, yield_with_no_args
- to_not alias

Author: joeldrapper