Testing for leftFisher.pm
-------------------------

Satanjeev Banerjee
bane0025@d.umn.edu

13th February, 2002

1. Introduction: 
----------------

We have tested leftFisher.pm, a component of Bigram Statistics Package
version 0.5. File leftFisher.pm implements the left fisher measure of
association. Note that leftFisher.pm is not a program by itself, but
is a statistical library package that is plugged into statistic.pl. We
test here the features of leftFisher.pm by running statistic.pl.

Following is a description of the aspects of leftFisher.pm that we
have tested. We provide the scripts and files used for testing so that
later versions of leftFisher.pm can be tested for backward
compatibility.


2. Phases of Testing: 
---------------------

We have divided the testing into two main phases: 

Phase 1: Testing leftFisher.pm's response to erroneous conditions. 
Phase 2: Testing leftFisher.pm's behaviour under normal conditions. 


2.1. Phase 1: Testing leftFisher.pm's response to erroneous conditions:
----------------------------------------------------------------------

The script for this phase is 'error-handling.sh'. To run the tests
contained in this script, type "error-handling.sh" at the command
prompt. 

This script performs several subtests: 

2.1.1. Subtest 1: 
-----------------

LeftFisher.pm is meant only for bigrams. This test checks if
leftFisher.pm throws an error when provided with larger n-grams.

2.1.2. Subtest 2: 
-----------------

LeftFisher.pm requires three frequency values: the frequency of the
bigram, and the two marginal totals (number of bigrams with the token
on the left and number of bigrams with the total on the right). If
these are not provided, leftFisher.pm should throw an error. This test
checks for this error.

2.1.3. Subtest 3: 
-----------------

The total number of bigrams in the file should be 1 or more. This test
checks if leftFisher.pm does indeed throw an error when passed a total
bigrams value that is less than or equal to zero.

2.1.4. Subtest 4: 
-----------------

The numbers passed to leftFisher.pm should be "valid" in that they
should represent a possible two-by-two table. If this is not the case,
various warnings are thrown by leftFisher.pm. This test checks for
these warnings.

Following is the input file, test-1.sub-4.cnt: 

17
one<>two<>-1 13 7
one<>three<>18 13 5
one<>four<>10 6 12
two<>two<>10 12 6
two<>four<>1 3 5
three<>four<>1 -1 5
three<>one<>1 18 5
four<>five<>1 1 -1
three<>five<>1 1 18
three<>seven<>1 0 0

The first bigram, "one<>two<>" should elicit a warning that a
frequency value cannot be negative. The next bigram, "one<>three<>"
should elicit the warning that the frequency value (18) cannot exceed
the total number of bigrams. The third bigram, "one<>four<>" should
result in a warning that the frequency value of the bigram (10) cannot
exceed the marginal totals (12). Similarly for the next bigram. The
fifth bigram, "two<>four<>" has no problems and should be calculated
for. The sixth bigram "three<>four<>" must not have a negative value
for the marginal total, the seventh bigram "three<>one<>" has too
large a marginal value (18) since it exceeds the total number of
bigrams, the eighth bigram has a negative marginal total value and the
ninth bigram, "three<>five<>" has too large a marginal total. Finally,
the last bigram "three<>seven<>" again has its bigram frequency
greater than the marginal frequencies.


2.2. Phase 2: Testing leftFisher.pm's behaviour under normal conditions:
------------------------------------------------------------------

The script for this phase is 'normal-handling.sh'. To run the tests
contained in this script, type "normal-handling.sh" at the command
prompt.

This script performs a single subtest that checks two things: 

First, it checks if leftFisher.pm works when the frequencies are given
in a non default order. All three frequency values are required,
however they could be in any order. Subtest a checks to see what
happens when the frequencies are in the default order (0-1, 0, 1) and
subtest b checks the situation when they are in a different order (0,
1, 0-1).

Second it checks the actual calculations of leftFisher.pm. The output
target files, test-2.sub-1-a.reqd and test-2.sub-1-b.reqd, have been
checked manually to see if the scores obtained are correct.


3. Conclusions:
---------------

Statistical library package leftFisher.pm has been tested for
erroneous conditions and normal operations too. It works! These tests
can be used to check for backward compatibility of newer versions.