= Overview
MSpec is a specialized framework that is syntax-compatible with RSpec for
basic things like +describe+, +it+ blocks and +before+, +after+ actions. MSpec
contains additional features that assist in writing the RubySpecs used by
multiple Ruby implementations.
MSpec attempts to use the simplest Ruby language features so that beginning
Ruby implementations can run the Ruby specs. So, for example, there is not
great concern given to constant clashes. Namespacing (or module scoping) is
not used because implementing this correctly took a significant amount of work
in Rubinius and it is likely that other implementations would also face
difficulties.
MSpec is not intended as a replacement for RSpec. MSpec attempts to provide a
subset of RSpec's features in some cases and a superset in others. It does not
provide all the matchers, for instance. However, MSpec provides several
extensions to facilitate writing the Ruby specs in a manner compatible with
multiple Ruby implementations.
First, MSpec offers a set of guards to control execution of the specs. These
guards not only enable or disable execution but also annotate the specs with
additional information about why they are run or not run. Second, MSpec
provides a different shared spec implementation specifically designed to ease
writing specs for the numerous aliased methods in Ruby. The MSpec shared spec
implementation should not conflict with RSpec's own shared behavior facility.
Third, MSpec provides various helper methods to simplify some specs, for
example, creating temporary file names. Finally, MSpec has several specialized
runner scripts that includes a configuration facility with a default project
file and user-specific overrides.
Caveats:
* Use RSpec to run the MSpec specs. There are no plans currently to make
  the MSpec specs runnable by MSpec.
* Don't mock the #hash method as MSpec's Mock implementation uses Hash
  internally. This can be replaced if necessary, but at this point there is no
  compelling need to do so.
== Architecture
== Matchers
Matchers are additional aids for the verification process. The default
is of course to #should or #should_not using the #== operator and its
friends but the matchers add a new set of 'operators' to help in the
task. They reside in `mspec/matchers/`. There are two broad categories,
those that apply to an individual object and those that apply to a
block:
=== Object
- `base` implements the standard #==, #< #<= #>= #> and #=~ with their
  normal semantics for the objects that you invoke them on.
- `be_ancestor_of` is equivalent to checking `obj.ancestors.include?`.
- `be_close` is a "delta" for floating-point math. Due to the very
  nature of it, floating-point comparisons should never be treated as
  exact. By default the tolerance is 0.00003 but it can be altered if
  so desired. So `0.23154.should be_close(0.23157)` would succeed
  (which is usually close enough for floating point unless you are
  doing some scientific computing.)
- `be_empty` checks `obj.empty?`
- `be_kind_of` is equivalent to `obj.kind_of?`
- `include` is `obj.include?`
=== Block
All of these should be applied to a block created with `lambda` or `proc`:
- `complain` is probably clearer stated as `lambda {...}.should complain`;
  it checks that the block issues a warning. The message can be checked
  against either a String or a Regexp.
- `output` checks that the block produces the given output (stdout as well
  as stderr, in that order) matched either to a String or a Regexp. This one
  uses overrides so if that is a problem (for e.g. speccing Readline or
  something) see below.
- `output_to_fd` is a lower-level version and actually verifies that output
  to a certain file descriptor is correct whether from an in-/output stream
  or an actual file. Also can check with either a String or a Regexp.
- `raise_error` verifies the exception type (if any) raised by the block it
  is associated with. The exception class can be given for finer-grained
  control (inheritance works normally so Exception would catch everything.)
== Nested 'describe' blocks
MSpec supports nesting one 'describe' block inside another. The examples in
the nested block are evaluated with all the before/after blocks of all the
containing 'describe' blocks. The following example illustrates this:
describe "Some#method" do
  before :each do
    @obj = 1
  end
  describe "when passed String" do
    before :each do
      @meth = :to_s
    end
    it "returns false" do
      # when this example is evaluated, @obj = 1 and @meth = :to_s
    end
  end
end
The output when using the SpecdocFormatter (selected with -fs to the runners)
will be as follows:
Some#method when passed String
- returns false
== Shared 'describe' blocks
MSpec supports RSpec-style shared 'describe' blocks. MSpec also provides a
convenience method to assist in writing specs for the numerous aliased methods
that Ruby provides. The following example illustrates shared blocks:
describe :someclass_some_method, :shared => true do
  it "does something" do
  end
end
describe "SomeClass#some_method" do
  it_should_behave_like "someclass_some_method"
end
The first argument to 'describe' for a shared block is an object that
duck-types as a String. The representation of the object must be unique. This
example uses a symbol. This was the convention for the previous facility that
MSpec provided for aliased method (#it_behaves_like). However, this convention
is not set in stone (but the uniqueness requirement is). Note that the
argument to the #it_should_behave_like is a String because at this time RSpec
will not find the shared block by the symbol.
MSpec continues to support the #it_behaves_like convenience method for
specifying aliased methods. The syntax is as follows:
it_behaves_like :symbol_matching_shared_describe, :method [, :object]
describe :someclass_some_method, :shared => true do
  it "returns true" do
    obj.send(@method).should be_true
  end
  it "returns something else" do
    @object.send(@method).should be_something_else
  end
end
# example #1
describe "SomeClass#some_method" do
  it_behaves_like :someclass_some_method, :other_method
end
# example #2
describe "SomeOtherClass#some_method" do
  it_behaves_like :someclass_some_method, :some_method, OtherClass
end
The first form above (#1) is used for typical aliases. That is, methods with
different names on the same class that behave identically. The
#it_behaves_like helper creates a before(:all) block that sets @method to
:other_method. The form of the first example block in the shared block
illustrates the typical form of a spec for an aliased method.
The second form above (#2) is used for methods on different classes that are
essentially aliases, even though Ruby does not provide a syntax for specifying
such methods as aliases. Examples are the methods on File, FileTest, and
File::Stat. In this case, the #it_behaves_like helper sets both @method and
@object in the before(:all) block (@method = :some_method, @object =
OtherClass in this example).
For shared specs that fall outside of either of these two narrow categories,
use nested or shared 'describe' blocks as appropriate and use the
#it_should_behave_like method directly.
== Guards
Since Ruby is not completely isolated from its platform or execution environment, the spec files may contain guards: 
conditions placed around a spec or a set of specs to enable or disable them. 
You can find an overview of the current guards and their usage in: https://rubyspec.org/wiki/mspec/Guards .
== Helpers
== Runners