Should and != operator

I’ve tried searching around for something describing how the #should
method works with the != operator, but couldn’t find anything
conclusive. Can someone please explain while the following lines will
pass if placed into an rspec example?

it “should fail but passes” do
[].should != []
‘some string’.should != ‘some string’
end

Thanks!
Willy

Willy…

Should you not use .should_not ?

– Lee

2009-10-12 11:33, Willy Mene:

I’ve tried searching around for something describing how the #should
method works with the != operator

Afaik it doesn’t. I have led to believe this is because there is no
method ‘!=’. Expression x!=y is instead just syntactic sugar for
!(x==y).

it “should fail but passes” do
[].should != []
‘some string’.should != ‘some string’
end

How about

it “fails now” do
[].should_not == []
‘some string’.should_not == ‘some string’
end

Looks like an rspec bug to me.

Bret

Afaik, != is one of the few operators that is intrinsic. I believe
there is no !=() method defined in Ruby.

Hunted and pecked from my iPhone

Yes, I do know about .should_not, and the example should be written
that way. So the following

[].should_not == []
‘string’.should_not == ‘string’

do fail. But I’m trying to understand why they pass with .should !=

Willy

2009-10-12 22:18, Tero T.:

Expression x!=y is instead just syntactic sugar for !(x==y).

To illustrate how this affects #should, think of

‘some string’.should != ‘some string’

Now Ruby internals kick in and desugar this (before anything is even
executed) to

!(‘some string’.should == ‘some string’)

Which obviously does not fail.

It’s not a bug. Consider:

“abc”.should eql(“abc”) <= pass
“abc”.should_not eql(“def”) <= pass

But eql() is a Ruby method. In Pickaxe, you’ll see that other
comparators such as != >= etc. Are not implemented as overridable
methods.

Hope this clarifies.

Hunted and pecked from my iPhone

On Oct 12, 2009, at 12:11 PM, Bret P. [email protected]

On 12 Oct 2009, at 19:33, Willy Mene wrote:

it “should fail but passes” do
[].should != []
‘some string’.should != ‘some string’
end

This is a common mistake, and one I made for a long while even after
being familiar with RSpec. I wonder if there is justification for an
AST pass over spec files to catch this (among possibly other issues)?

Just one of my usual idle thoughts…

Ashley


http://www.patchspace.co.uk/
http://www.linkedin.com/in/ashleymoran

Den 12. okt. 2009 kl. 21.11 skrev Bret P. [email protected]nvalid:

Looks like an rspec bug to me.

It’s not an rspec bug. != is not a method, and therefore can’t be
treated by rspec. It’s a limitation of ruby.

Aslak

Aslak Hellesøy wrote:

Den 12. okt. 2009 kl. 21.11 skrev Bret P. [email protected]:

Looks like an rspec bug to me.

It’s not an rspec bug. != is not a method, and therefore can’t be
treated by rspec. It’s a limitation of ruby.
OK. I get it.

Bret

On Mon, Oct 12, 2009 at 3:18 PM, Tero T. [email protected] wrote:

2009-10-12 11:33, Willy Mene:

I’ve tried searching around for something describing how the #should
method works with the != operator

Afaik it doesn’t. Â I have led to believe this is because there is no
method ‘!=’. Â Expression x!=y is instead just syntactic sugar for
!(x==y).

This is not true in Ruby 1.9. You can define != separate from ==.

Best,
Michael G.

On Mon, Oct 12, 2009 at 5:03 PM, Ashley M.
[email protected] wrote:

This is a common mistake, and one I made for a long while even after being
familiar with RSpec. I wonder if there is justification for an AST pass
over spec files to catch this (among possibly other issues)?

The AST pass over the spec files already exists. It’s what Ruby does
when you run the specs, and these quirks are caught when your specs
pass and you haven’t done anything to make them pass yet. >8->

(You do always start with failing specs, and then do the work to
make them pass, right?)


Have Fun,
Steve E. (removed_ema[email protected])
ESCAPE POD - The Science Fiction Podcast Magazine
http://www.escapepod.org

On 14 Oct 2009, at 02:25, Stephen E. wrote:

The AST pass over the spec files already exists. It’s what Ruby does
when you run the specs, and these quirks are caught when your specs
pass and you haven’t done anything to make them pass yet. >8->

Really? I just tried `1.should != 2’ and got no warnings.

(You do always start with failing specs, and then do the work to
make them pass, right?)

Only when I care if the code does something useful =)

Ashley


http://www.patchspace.co.uk/
http://www.linkedin.com/in/ashleymoran

On Wed, Oct 14, 2009 at 4:34 AM, Ashley M.
[email protected] wrote:

On 14 Oct 2009, at 02:25, Stephen E. wrote:

[…] these quirks are caught when your specs
pass and you haven’t done anything to make them pass yet. >8->

Really? I just tried `1.should != 2’ and got no warnings.

Did your brain try to warn you? You’re part of the system, you know.

8->

(You do always start with failing specs, and then do the work to
make them pass, right?)

Only when I care if the code does something useful =)

If you don’t care whether the code is useful, I’m baffled as to why
you might care whether the tests are useful.


Have Fun,
Steve E. ([email protected])
ESCAPE POD - The Science Fiction Podcast Magazine
http://www.escapepod.org

On 14 Oct 2009, at 17:01, Stephen E. wrote:

Did your brain try to warn you? You’re part of the system, you
know. >8->

Well I already know not to do should !=, so I don’t do it. But I
was suggesting that RSpec could make an AST pass over the specs to
pick up this, which is undetectable otherwise - at least under Ruby
<1.9, apparently. (It would be something like mini RSpecLint, I
guess.) != caught me out quite a few times when I was first learning
RSpec. I misinterpreted your comment to mean that something like this
was already in RSpec.

If you don’t care whether the code is useful, I’m baffled as to why
you might care whether the tests are useful.

Lol, I was joking! The implication was I always write specs* because
I always care if the code is useful.

Ashley

  • Actually, that’s a lie. I have support code in my Cucumber features
    that has no specs, and yes, we’ve found bugs in them. But all my non-
    false-positive features prove that they work =) So maybe I should
    say, “I always write specs except when I don’t, and I always regret it
    when I don’t”.


http://www.patchspace.co.uk/
http://www.linkedin.com/in/ashleymoran

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