[Wtr-general] Trying to understand the UnitTests directorymanipulation

[Cain, Mark]

This is right out of the pickaxe 2nd edition pages 336 - 337.

 

__FILE__          String               The name of the current source
file. [r/o]

 

The constant __FILE__ and the variable $0 are often used together to run
code only if it appears in the file run directly by the user.  For
example, library writers often use this to include tests in their
libraries that will run if the library source is run directly, but not
if the source is required into another program.

            

# Library code

            #...

            If __FILE__ == $0

                        #tests ...

            end

 

--Mark

 

________________________________

From: wtr-general-bounces at rubyforge.org
[mailto:wtr-general-bounces at rubyforge.org] On Behalf Of Paul Carvalho
Sent: Thursday, April 20, 2006 12:05 PM
To: wtr-general at rubyforge.org
Subject: [Wtr-general] Trying to understand the UnitTests
directorymanipulation

 

I'm finally getting around to taking a closer look at the Watir
UnitTests and thought that I would start with the 'all_tests.rb' and
'core_tests.rb' scripts.  I'm having some trouble trying to understand
*why* the paths are manipulated the way they are. 

Both files are basically the same, just the [variable] list of test
files called is different.  Here's the 'all_tests.rb' script:
--- 
TOPDIR = File.join(File.dirname(__FILE__), '..')
$LOAD_PATH.unshift TOPDIR 

require 'unittests/setup.rb'

Dir.chdir TOPDIR
$all_tests.each {|x| require x}
---

Here's my understanding of what this script is doing:

1) Line one sets the variable = './..'   ( using a much more verbose way
of doing it  ;) ) 
- Incidentally, I was unable to find any reference to the use of
'__FILE__' anywhere.  Is that some special kind of dummy variable?  Can
someone please tell me how/why this works?

2) Line two prepends './..' to the Ruby load path 
- I don't understand the design choice behind this.  i.e. I don't know
why the first two lines can't just be squished into this one line - as
in:
   $LOAD_PATH.unshift './..'
( I must be missing something important further down the scripts that I
haven't gotten to yet. ) 

3) skip line three for the moment..

4) Line four changes the current directory to the parent of the current
(i.e. essentially 'cd ..')

5) Back to Line three - now that we are one directory back/up, let's
_require_ the file that *used to be* in the current directory, but now
is in the subdirectory called 'unittests' 

6) Finally, call/require all the test files (where each element in the
variable array contains the path 'unittests/' before the filename)

Did I get that right?

So my question is this:
- Why do the UnitTest scripts go to all the trouble of prepending the
parent path to the Ruby Load Path, then change to the parent path, only
to then call all the files in the desired subdirectory? 

Is there something that I'm missing regarding the value of directory
*position* when running Ruby/Watir scripts?  I am not doing this
directory one-two step in my scripts and am wondering if it is something
that I should add or not. 

Please let me know what I am missing here.  Thanks.

Paul.



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