How to run PHPUnit test suite with bootstrap file with phing?

My app structure:

```
application/
library/
tests/
  application/
  library/
  bootstrap.php
  phpunit.xml
build.xml

```

phpunit.xml:

```
<phpunit bootstrap="./bootstrap.php" colors="true">
    <testsuite name="Application Test Suite">
        <directory>./</directory>
    </testsuite>
    <filter>
        <whitelist>
            <directory
              suffix=".php">../library/</directory>
            <directory
              suffix=".php">../application/</directory>
            <exclude>
                <directory
                  suffix=".phtml">../application/</directory>
            </exclude>
        </whitelist>
    </filter>
</phpunit>

```

then:

```
cd /path/to/app/tests/
phpunit
#all test passed

```

But how do I run the tests from `/path/to/app/` dir? The problem is, that the `bootstrap.php` depends on relative paths to library and application. 

If I run `phpunit --configuration tests/phpunit.xml /tests` I got a bunch of file not found errors.

How do I write `build.xml` file for `phing` to run the tests the same way `phpunit.xml` does?