Mocking the shell command (Kernel module)

Testing RSpec
1

hello there,
what is the best (or any) way of mocking the running of shell commands?

e.g.
code like the following:

%{ ls }

spec:

it “should list the directory contents”
shell = mock(Object) # %{} lives in Kernel module and its sugar for `

end

2

ooopssss, sorry the last one goes out unfinished (some gmail hotkey)…

hello there,
what is the best (or any) way of mocking the running of shell commands?

e.g.
code like the following:

def method
%{ ls }
end

spec:

it “should list the directory contents”
shell = mock(Object) # %{} lives in Kernel module and its sugar for shell.should_receive(:).with(:ls)
end

sorry about latter one, thanks in advance
joaquin

2008/9/12 Joaquin Rivera P. [email protected]

3

On 12 Sep 2008, at 14:12, Joaquin Rivera P. wrote:

spec:

it “should list the directory contents”
shell = mock(Object) # %{} lives in Kernel module and its sugar
for shell.should_receive(:).with(:ls)
end

sorry about latter one, thanks in advance
joaquin

I suggest you put a ‘seam’ between your code and the call the Kernel.

See Pat’s excellent answer to a similar question in this thread:
http://www.ruby-forum.com/topic/164893#new

cheers,
Matt

http://blog.mattwynne.net

In case you wondered: The opinions expressed in this email are my own
and do not necessarily reflect the views of any former, current or
future employers of mine.

4

On Sep 12, 2008, at 9:29 AM, Matt W. wrote:

end
joaquin

I suggest you put a ‘seam’ between your code and the call the Kernel.

That sounds like a good idea. You can also Kernel#directly (instead offoocall Kernel.send(:, “foo”). This allows you to stub out
Kernel#`.

Scott

5

thanks,
I’ll give that a try

joaquin

2008/9/12 Matt W. [email protected]

6

hi,
this did the trick:

class Shell
def self.sh command
%{ command }
end
end

then I am able to:

it “should be mock alright” do
Shell.should_receive(…).with(…)
end

is that correct so?

sorry aboout latter one (gotta do something about that hotkeys sendind
my
mails all of a sudden)

thanks guys
joaquin

2008/9/13 Joaquin Rivera P. [email protected]

7

hi,
this did the trick:

class Shell
def self.sh command
%{ command }
end
end

then I am able to:

it “should be mock alright” do

end

2008/9/13 Scott T. [email protected]

8

On 13 Sep 2008, at 13:42, Joaquin Rivera P. wrote:

it “should be mock alright” do
Shell.should_receive(…).with(…)
end

is that correct so?

You’ve definitely got the idea, and that will work nicely for the
examples you’ve given.

You might find that the code will reveal its intent a little better,
and result in more readable specs if you think about exactly what
role you want the shell to play for you in this particular instance,
and create your shell-wrapping object with the specific methods that
role needs to provide rather than a one-size-fits-all method as you
have done here.

So, for example, if I want to be able to get and commit files from a
source control repository, I can create a class like

class GitSourceControl
def checkout(file)
%x{ git checkout #{file} }
end
end

This gives me a couple of advantages:

Firstly, my spec for the object which depends on the shell commands,
looks like this:

it “should checkout the file” do

filename = “blah”
GitSourceControl.should_receive(:checkout).with(filename)

… exercise the object under test…

Which is very readable and clear.

Secondly, if I ever want to change the type of source control I’m
using, I can just write another class that implements the same
interface - and swap out GitSourceControl for,
SubversionSourceControl, say.

Does that make sense?

class Shell

e.g.
shell.should_receive(:`).with(:ls)

rspec-users mailing list
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cheers,
Matt

http://blog.mattwynne.net

In case you wondered: The opinions expressed in this email are my own
and do not necessarily reflect the views of any former, current or
future employers of mine.

9

cool, thanks

2008/9/13 Matt W. [email protected]