test the return value of a method that triggers an error with PHPUnit

This question is specific to using PHPUnit.

PHPUnit automatically converts php errors to exceptions. Is there a way to test the return value of a method that happens to trigger a php error (either built-in errors or user generated errors via trigger_error)?

Example of code to test:

function load_file ($file)
{
    if (! file_exists($file)) {
        trigger_error("file {$file} does not exist", E_USER_WARNING);
        return false;
    }
    return file_get_contents($file);
}

This is the type of test I want to write:

public function testLoadFile ()
{
    $this->assertFalse(load_file('/some/non-existent/file'));
}

The problem I am having is that the triggered error causes my unit test to fail (as it should). But if I try to catch it, or set an expected exception any code that after the error is triggered never executes so I have no way of testing the return value of the method.

This example doesn't work:

public function testLoadFile ()
{
    $this->setExpectedException('Exception');
    $result = load_file('/some/non-existent/file');

    // code after this point never gets executed

    $this->assertFalse($result);
}

Any ideas how I could achieve this?