17 Jun 2012

RSpecのequal, eql, eq, be の違い

RSeqでshould equalと書くべきかeqlと書くべきか、それともbeと書くべきか時々混乱するのでこの際覚えてしまおうと意味で何がちがうんだろうと見てみた。それによるとごく簡単にまとめると以下のような結果だった。

二つの変数を比較するとき；


  • 変数の値だけを比べる
    • eql eq
  • 変数の値だけでなく、インスタンスのobject_idまで比べる
    • equal be
と、ここまで覚えておけばSpec書くのに支障はない。


もう少し掘り下げると、それぞれ以下のような仕組みになっている。

eql

Matcherの場所はここ。実際にはObject#eql?を呼んでいる。

> arr.eql? :a => 1, :b => 2
=> true


equal

Matcherの場所はここ。実際にはObject#equal?を呼んでいる

> arr.equal? :a => 1, :b => 2
=> false


eq

eqの定義はDSLの方にあるらしい。


be

Matcherの定義はここ。beに引数があればBeSameAs#matches?がshouldによって呼ばれる仕組みになっている。




整理して実際に試してみよう。以下のようにString, Array, Fixnumの型のインスタンスについてそれぞれeq, eql, equal, beのマッチャでSpecを実施してみた。

# ./tmp_spec.rb
require 'rspec'

describe 'eq' do
  it('should find two strings are equal') { "".should eq ""}
  it('should find two Arrays are equal') { {:a => 1}.should eq :a => 1 }
  it('should find two Fixnums are equal') { 1.should eq 1 }
end

describe 'eql' do
  it('should find two strings are equal') { "".should eql ""}
  it('should find two Arrays are equal') { {:a => 1}.should eql :a => 1 }
  it('should find two Fixnums are equal') { 1.should eql 1 }
end

describe 'equal' do
  it('should find two Strings are equal') { "".should equal ""}
  it('should find two Arrays are equal') { {:a => 1}.should equal :a => 1 }
  it('should find two Fixnums are equal') { 1.should equal 1 }
end

describe 'be' do
  it('should find two strings are equal') { "".should be ""}
  it('hould find two Arrays are equal') { {:a => 1}.should be :a => 1 }
  it('should find two Fixnums are equal') { 1.should be 1 }
end


結果は以下のとおり。equalとbeでは　String, Arrayではobject_idまで同じかチェックしている。
$ rspec tmp_spec.rb -f doc

eq
  should find two strings are equal
  should find two Arrays are equal
  should find two Fixnums are equal

eql
  should find two strings are equal
  should find two Arrays are equal
  should find two Fixnums are equal

equal
  should find two Strings are equal (FAILED - 1)
  should find two Arrays are equal (FAILED - 2)
  should find two Fixnums are equal

be
  should find two strings are equal (FAILED - 3)
  hould find two Arrays are equal (FAILED - 4)
  should find two Fixnums are equal

Failures:

  1) equal should find two Strings are equal
     Failure/Error: it('should find two Strings are equal') { "".should equal ""}
       
       expected # => ""
            got # => ""
       
       Compared using equal?, which compares object identity,
       but expected and actual are not the same object. Use
       'actual.should == expected' if you don't care about
       object identity in this example.
     # ./tmp_spec.rb:16:in `block (2 levels) in '

  2) equal should find two Arrays are equal
     Failure/Error: it('should find two Arrays are equal') { {:a => 1}.should equal :a => 1 }
       
       expected # => {:a=>1}
            got # => {:a=>1}
       
       Compared using equal?, which compares object identity,
       but expected and actual are not the same object. Use
       'actual.should == expected' if you don't care about
       object identity in this example.
       
       
       Diff:{:a=>1}.==({:a=>1}) returned false even though the diff between {:a=>1} and {:a=>1} is empty. Check the implementation of {:a=>1}.==.
     # ./tmp_spec.rb:17:in `block (2 levels) in '

  3) be should find two strings are equal
     Failure/Error: it('should find two strings are equal') { "".should be ""}
       
       expected # => ""
            got # => ""
       
       Compared using equal?, which compares object identity,
       but expected and actual are not the same object. Use
       'actual.should == expected' if you don't care about
       object identity in this example.
     # ./tmp_spec.rb:22:in `block (2 levels) in '

  4) be hould find two Arrays are equal
     Failure/Error: it('hould find two Arrays are equal') { {:a => 1}.should be :a => 1 }
       
       expected # => {:a=>1}
            got # => {:a=>1}
       
       Compared using equal?, which compares object identity,
       but expected and actual are not the same object. Use
       'actual.should == expected' if you don't care about
       object identity in this example.
       
       
       Diff:{:a=>1}.==({:a=>1}) returned false even though the diff between {:a=>1} and {:a=>1} is empty. Check the implementation of {:a=>1}.==.
     # ./tmp_spec.rb:23:in `block (2 levels) in '

Finished in 0.01339 seconds
12 examples, 4 failures

Failed examples:

rspec ./tmp_spec.rb:16 # equal should find two Strings are equal
rspec ./tmp_spec.rb:17 # equal should find two Arrays are equal
rspec ./tmp_spec.rb:22 # be should find two strings are equal
rspec ./tmp_spec.rb:23 # be hould find two Arrays are equal


でもこのFixnumの比較に関しては Specが成功してしまう。
describe 'be' do
  it('should find two Fixnums are equal') { 1.should be 1 }
end

これはFixnumのidがrubyを起動時に実行されて既に予約済みだからのようだ

irb/ pry
[28] pry(main)> 1.object_id
=> 3
[29] pry(main)> 2.object_id
=> 5
[30] pry(main)> 3.object_id
=> 7
[35] pry(main)> 1.object_id
=> 3


[32] pry(main)> 1.0.object_id
=> 105431370

このようにFixnumのインスタンスはシングルトンで定義されているようだ。
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