Mocking a method with a block

[Fernando Guillen]

Hi people,

I have an application that download emails from an email account an
process them.

What I would like to do is to mock the mail download petition and not
process the real mails but an array of mails I have for this propos.

This is the precise situation: I have this:

Net::POP3.start( opts[:server], port, opts[:user], opts[:pass] )
do |pop|
pop.each_mail do |m|
block.call( m )
end
end

I would like to have a mock that if on my test call to

=> Net:OP3.start( opts[:server], port, opts[:user], opts[ass] ) do
|pop|

Not any mailing petition is done but the body of the method is still
working but not with real mails but with an array of fake mails like
this:

=> mails = [ File.read('/dir/mail1.raw_mail'),
File.read('/dir/mail2.raw_mail')]

Is this possible?.. am I completely lost?.. is there any better way to
do this?

Any suggestion is welcome.

Thanks

f.

 

[Jesús Gabriel y Galán]

Hi people,

I have an application that download emails from an email account an
process them.

What I would like to do is to mock the mail download petition and not
process the real mails but an array of mails I have for this propos.

This is the precise situation: I have this:

=A0 =A0 =A0Net::POP3.start( opts[:server], port, opts[:user], opts[:pass]= )
do |pop|
=A0 =A0 =A0 =A0pop.each_mail do |m|
=A0 =A0 =A0 =A0 =A0block.call( m )
=A0 =A0 =A0 =A0end
=A0 =A0 =A0end

I would like to have a mock that if on my test call to

=3D> Net:OP3.start( opts[:server], port, opts[:user], opts[ass] ) do
|pop|

Not any mailing petition is done but the body of the method is still
working but not with real mails but with an array of fake mails like
this:

=3D> mails =3D [ File.read('/dir/mail1.raw_mail'),
File.read('/dir/mail2.raw_mail')]

Is this possible?.. am I completely lost?.. is there any better way to
do this?

One option would be to change the start method of Net:OP3 to do
exactly what you describe.
Remember that Ruby is open and you can redefine any method on any
class. You can always alias the method start before changing it, so
you can revert to the original definition after the test.

Jesus.

 

[Fernando Guillen]

One option would be to change the start method of Net:OP3 to do
exactly what you describe

This is a good idea.

I can open the class Net:OP3 and redefine the method .start.

Now, how can I organize this to charge the redefinition of the method at
the beginning of the test and revert it at the end of the test.

I mean, if I have a file that redefine the Net:OP3.start method I can
'require' it but I don't know how to 'un-require' it.

Also I would like to simulate that the Net:OP3.start charges my mails
array (different on every test) and if I redefine this method in a
generic way I don't know how to use my mails array inside the redefined
method.

Example, if I have my own redefinition of the method like:

class Net::POP3
def self.start( *, &block )

(How can I put my mails array in here?)

end
end

I think I need some kind of mocking tutorial or something, if you know
any one and you can offer me the link it will be great.

Thanks

f.

 

[Jesús Gabriel y Galán]

This is a good idea.

I can open the class Net:OP3 and redefine the method .start.

Now, how can I organize this to charge the redefinition of the method at
the beginning of the test and revert it at the end of the test.

You can use alias_method to "save" a copy of the original method with
another name. You can do this in the setup of your tests, and revert
back to that version in the teardown:

irb(main):001:0> class A
irb(main):002:1> def self.test
irb(main):003:2> "original test"
irb(main):004:2> end
irb(main):005:1> end

irb(main):013:0> class A
irb(main):014:1> class << self
irb(main):015:2> alias_method rig_test, :test
irb(main):016:2> end
irb(main):017:1> end

# at this point you can call A.test and A.orig_test and both do the same
# now you can create a new version of the method:

irb(main):020:0> class A
irb(main):021:1> def self.test
irb(main):022:2> "new test, original was [#{orig_test}]"
irb(main):023:2> end
irb(main):024:1> end
=3D> nil
irb(main):025:0> A.test
=3D> "new test, original was [original test]"
irb(main):026:0> A.orig_test
=3D> "original test"

As you can see, you can still refer to the original method. To put it back:

irb(main):027:0> class A
irb(main):028:1> class << self
irb(main):029:2> alias_method :test, rig_test
irb(main):030:2> end
irb(main):031:1> end
=3D> #<Class:A>
irb(main):032:0> A.test
=3D> "original test"

(this leaves the orig_test method around, but I don't think that would
be a problem).

I mean, if I have a file that redefine the Net:OP3.start method I can
'require' it but I don't know how to 'un-require' it.

Also I would like to simulate that the Net:OP3.start charges my mails
array (different on every test) and if I redefine this method in a
generic way I don't know how to use my mails array inside the redefined
method.

If this is just for running a test you could use a global variable or
a constant:

irb(main):034:0> MY_EMAILS =3D %w{a b c d e}
=3D> ["a", "b", "c", "d", "e"]
irb(main):035:0> class A
irb(main):036:1> class << self
irb(main):037:2> alias_method rig_test, :test
irb(main):038:2> def test
irb(main):039:3> "my emails: #{MY_EMAILS}"
irb(main):040:3> end
irb(main):041:2> end
irb(main):042:1> end
=3D> nil
irb(main):043:0> A.test
=3D> "my emails: abcde"

You can also look at class_eval and define_method to build a closure
around your emails' variable (sorry, don't have time now to do that,
I'll come back later if you need it).

Jesus.

 

[Fernando Guillen]

Jesús, Thank you so much for your help.

I think I have enough information to work by my self.

Thanks for your work.

f.

 

[Brian Candler]

Is this possible?.. am I completely lost?.. is there any better way to
do this?

I'd suggest you use an existing mocking library like "mocha". Example:

-------- 8< ----------------
require 'net/pop'
require 'test/unit'
require 'rubygems'
require 'mocha'

# code to test
class Foo
attr_reader pts
def initialize(opts)
@opts = opts
end
def bar(block)
Net:OP3.start( opts[:server], opts[ort], opts[:user],
opts[ass] ) do |pop|
pop.each_mail do |m|
block.call( m )
end
end
end
end

# tests
class MyTest < Test::Unit::TestCase
def test_1
mails = ["xxxxx","yyy"]
mockpop = mock
mockpop.expectseach_mail).multiple_yields(*mails)
Net:OP3.expectsstart).with("127.0.0.1", 110, "a",
"b").yields(mockpop)

foo = Foo.newserver=>"127.0.0.1", ort=>110, :user=>"a",
ass=>"b")
res = []
foo.bar(lambda { |x| res << x.size })
assert_equal [5,3], res
end

# more expectation-based style
def test_2
mails = ["xxxxx","yyy"]
mockpop = mock
mockpop.expectseach_mail).multiple_yields(*mails)
Net:OP3.expectsstart).with("127.0.0.1", 110, "a",
"b").yields(mockpop)

mockblock = mock
seq = sequenceblock)
mockblock.expectscall).with(mails[0]).in_sequence(seq)
mockblock.expectscall).with(mails[1]).in_sequence(seq)

foo = Foo.newserver=>"127.0.0.1", ort=>110, :user=>"a",
ass=>"b")
foo.bar(mockblock)
end
end
-------- 8< ----------------

I find there's something unsatisfying about tests which look like this.
Sometimes you can spend more effort on the mechanics of mocking than on
solving the original problem, and the resulting tests are closely
coupled to the internal implementation of your function. But that *is*
what you asked for

Refactoring might make your code easier to test. e.g.

-------- 8< ----------------
require 'net/pop'
require 'test/unit'
require 'rubygems'
require 'mocha'

class Foo
attr_reader pts
def initialize(opts)
@opts = opts
end
def bar(block)
for_all_messages do |m|
block.call(m)
end
end
private
def for_all_messages(&blk)
Net:OP3.start( opts[:server], opts[ort], opts[:user],
opts[ass] ) do |pop|
pop.each_mail(&blk)
end
end
end

class MyTest < Test::Unit::TestCase
def test_1
foo = Foo.new({})

mails = ["xxxxx","yyy"]
foo.expectsfor_all_messages).multiple_yields(*mails)
res = []
foo.bar(lambda { |x| res << x.size })
assert_equal [5,3], res
end
end
-------- 8< ----------------

HTH,

Brian.

 

[Fernando Guillen]

I'd suggest you use an existing mocking library like "mocha".

This was how I started to try mock the Net:OP3.

But instead of using the .yields method, that I didn't know about, I
tried to mock directly the Net:OP3.start method and this didn't work.

Thanks a lot for your comprehensive examples and also for the
re-factoring suggestion for an easier mock.

Best regards.

f.

 

[Brian Candler]

But instead of using the .yields method, that I didn't know about, I
tried to mock directly the Net:OP3.start method and this didn't work.

It would be really useful if you could attach arbitrary behaviour to a
mocked method - perhaps 'returns' with a block:

m = [1,2,3]
Net:OP3.expectsstart).returns { m.each { puts m }; m.size }

This is something I've missed badly in the past, and I've ended up
mocking directly using Object.new and defining singleton methods.

 

[Fernando Guillen]

Hi again people,

Following your suggestions I am trying to build an small library to
abstract this behavior on a reusable way:

* http://github.com/fguillen/NetPopMock

My problem now is that I'm not able to use the _raw_mails_ array sent on
the **NetPopMock.fake** call

See the test example:

*
http://github.com/fguillen/NetPopMock/blob/master/test/net_pop_mock_test.rb#L15

Into the mocked class:

* http://github.com/fguillen/NetPopMock/blob/master/net_pop_mock.rb#L30

Jesus was the first one suggesting me to use _class_eval_ and I told him
that I thought I was enough information to work on my self.. well that
was not true.. I need help again

I know the solution is in a mix of _eval_ and _binding_ but I don't find
it.

Thanks again

f.

 

[Fernando Guillen]

Thinking I found the solution:

*
http://github.com/fguillen/NetPopMock/commit/7003aa7db33f98165a10987058ece171a7b371dd

Do you think is a clean solution?

Regards

f.

 

[Fernando Guillen]

See the test example:

*
http://github.com/fguillen/NetPopMock/blob/master/test/net_pop_mock_test.rb#L15

Into the mocked class:

* http://github.com/fguillen/NetPopMock/blob/master/net_pop_mock.rb#L30

Sorry the links are not static, use this others:

*
http://github.com/fguillen/NetPopMo...e7487ee44c2b927/test/net_pop_mock_test.rb#L15

*
http://github.com/fguillen/NetPopMo...c870ef23cce7487ee44c2b927/net_pop_mock.rb#L30

 

[Fernando Guillen]

The history just finished with this:

* http://rubygems.org/gems/fibber_mailman

Any suggestion or comment will be welcome.

Thanks again

f.