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: rubyspec.org/wiki/mspec/Guards .

Helpers

Runners