PHPT is a test format designed for testing internal PHP functions.  But you can use it to test your own functions as well.

Essentially, the PHPT format consists of a few blocks of text marked by the following delimeters:

• --TEST--

• --FILE--

• --EXPECT--

Here’s an example:

#IncrementTest.php

--TEST--
increment() function - basic test for increment()

--FILE--
<?php
   $integer = increment(1);
   $string = increment("one");

   var_dump($integer);
   var_dump($string);
?>
--EXPECT--
int(2)
string(3) "two"

PHPT scripts are executed by “run-tests.php”

You can execute it with Pear:

pear run-tests IncrementTest.phpt

Running 1 tests
FAIL increment() function - a basic test to see if it works[IncrementTest.phpt]
wrote log to "C:\dev\eclipse\workspaces\aaron\MyTestClass\t\run-tests.log"
TOTAL TIME: 00:03
0 PASSED TESTS
0 SKIPPED TESTS
1 FAILED TESTS:
IncrementTest.phpt

You can see why it failed in the .diff file (which is a diff of the .exp and .out files.)  All the generated files are:

IncrementTest.diff -- this is a diff of the expected and actual output
IncrementTest.exp -- this is the expected output
IncrementTest.log -- this is the same test output sent to stdout (see above)
IncrementTest.out -- this is the actual output
IncrementTest.php -- this is the --FILE-- section of your test 
IncrementTest.phpt -- this is your original test
run-tests.log -- this is the summary of your test results (# of tests passed/failed/skipped)

PHPT test stubs can be autogenerated http://qa.php.net/autogenerate.php

php generate-phpt.php -f increment

Here’s a good introductory tutorial for PHPT: http://qa.php.net/write-test.php

Here’s the detailed PHPT spec http://qa.php.net/phpt_details.php