MiniTest: a curious case of include (1.8 vs 1.9)

Ruby
1

I’ve been messing around with minitest and came across something very
strange. Does anyone have an explanation for what is going on here?
I think it must indicate subtle differences in blocks between 1.8 and
1.9.

require ‘rubygems’
require ‘minitest/spec’

Including a module in a spec does not make constants

available under ruby 1.8 but it does under ruby 1.9.

This script requires the minitest gem to be installed:

% gem install minitest

module A
module B
end
end

This passes on ruby 1.9, but not on 1.8.

describe “MiniTest Includes” do
include A

it "should show inclusion works" do
  B.must_equal A::B
end

end

This passes on both. What’s more, if you uncomment this

spec, the assignment TRANSLATES to the “MiniTest Includes”

spec and that spec will pass!

describe “MiniTest Assigns” do

B = A::B

it “should show assignment works” do

B.must_equal A::B

end

end

Here is an example showing the assignment case works.

module X
module Y
end
end

describe “MiniTest Assigns X::Y” do
Y = X::Y

it "should show constant assignment works" do
  Y.must_equal X::Y
end

end

MiniTest::Unit.autorun

2

As an additional note to this, assigning constants in a describe under
1.8 causes namespace pollution.

require ‘rubygems’
require ‘minitest/spec’

module X
module Y
end
end

describe “Namespace Pollution” do
Y = X::Y
end

puts Y # => ‘X::Y’ on 1.8, error on 1.9

3

Hi –

On Fri, 30 Jan 2009, Simon C. wrote:

describe “Namespace Pollution” do
Y = X::Y
end

puts Y # => ‘X::Y’ on 1.8, error on 1.9

It’s not specific to minitest; it’s a change in how constants are
resolved. I’m not sure of the exact formulation but what’s happening
is that in a class_eval’d code block (which I think is what describe
does), 1.8 is looking for a constant scoped to the outer level, while
1.9 is looking for one that is scope to the class that’s being
class_evaled.

You can see this also with a block for a new class:

module A
module B
end
end

Class.new do
include A
p B == A::B # true in 1.9, error in 1.8 (unknown constant B)
end

David

–
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (The Well-Grounded Rubyist)

http://www.wishsight.com => Independent, social wishlist management!

4

It’s not specific to minitest; it’s a change in how constants are
resolved. I’m not sure of the exact formulation but what’s happening
is that in a class_eval’d code block (which I think is what describe
does), 1.8 is looking for a constant scoped to the outer level, while
1.9 is looking for one that is scope to the class that’s being
class_evaled.

Interesting. I expected it would be something like this. Kinda makes
specs hard to use under 1.8 IMO. You’re left with nesting describes
within a module, or using the full constant name.

module A
module B
end

describe "Nest in Module" do
  it "should show nesting works" do
    B.must_equal A::B
  end
end

end

describe “Full Constant Name” do
it “should show full names works” do
A::B.must_equal A::B
end
end

5

Hi –

On Fri, 30 Jan 2009, Simon C. wrote:

within a module, or using the full constant name.
end

describe “Full Constant Name” do
it “should show full names works” do
A::B.must_equal A::B
end
end

All it means is that you can’t make an assertion in the spec that
conflicts with how the language is engineered, and that’s always true
:slight_smile:

David

–
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (The Well-Grounded Rubyist)

http://www.wishsight.com => Independent, social wishlist management!

6

Here’s a workaround that combines the include call with a const_get
call. Can still use ‘describe’. Doesn’t pollute namespace. Works on
1.8 and 1.9. Not too ugly:

require ‘minitest/spec’
MiniTest::Unit.autorun

put this little method in some kind of spec_helper.rb file

module Kernel
def use(const, subconst)
self.instance_eval( “include #{const}” )
const.const_get(subconst)
end
end

module A
module B
end
end

describe ‘Includes’ do
B = use A, ‘B’

it 'shows inclusion working' do
  B.must_equal A::B
end

end

7

All it means is that you can’t make an assertion in the spec that
conflicts with how the language is engineered, and that’s always true
:slight_smile:

I guess there’s something to that. Here’s a good workaround that
doesn’t pollute and works on 1.8 and 1.9… evade the block by
foregoing describe.

module A
module B
end
end

This passes on both ruby 1.8 and 1.9 and doesn’t pollute.

class MiniTestIncludes < MiniTest::Spec
include A

it "should show inclusion works" do
  B.must_equal A::B
end

end