PHPUnit_Util_PHP::$phpBinary contains the path to the PHP
interpreter.
When not set, the following assumptions will be made:
1. When the PHP CLI/CGI binary configured with the PEAR Installer
(php_bin configuration value) is readable, it will be used.
2. When PHPUnit is run using the CLI SAPI and the $_SERVER['_']
variable does not contain the string "PHPUnit", $_SERVER['_']
is assumed to contain the path to the current PHP interpreter
and that will be used.
3. When PHPUnit is run using the CLI SAPI and the $_SERVER['_']
variable contains the string "PHPUnit", the file that $_SERVER['_']
points to is assumed to be the PHPUnit TextUI CLI wrapper script
"phpunit" and the binary set up using #! on that file's first
line of code is assumed to contain the path to the current PHP
interpreter and that will be used.
4. The current PHP interpreter is assumed to be in the $PATH and
to be invokable through "php".