Laravel 5.2 Mocked file upload unit test fails

I've just upgraded from Laravel 5.1 to 5.2 and previously successful tests are now failing, with "Perhaps an exception was thrown?"

There were 3 failures:

1) TRP\Nps\Tests\FileHandlerControllerTest::testCSVFileUploadImportsRecipients
Invalid JSON was returned from the route. Perhaps an exception was thrown?

/home/vagrant/Code/nps/vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/MakesHttpRequests.php:354
/home/vagrant/Code/nps/vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/MakesHttpRequests.php:316
/home/vagrant/Code/nps/vendor/laravel/framework/src/Illuminate/Foundation/Testing/Concerns/MakesHttpRequests.php:255
/home/vagrant/Code/nps/tests/FileHandlerControllerTest.php:56

Logging the actual response from the test itself, I see the following:

UploadedFile.php line 235: The file "FileHandlerCSV.csv"; was not uploaded due to an unknown error.

Which isn't overly helpful. My mockFileUpload method is as follows:

/**
 * Mock a file upload
 */
public function mockFileUpload($fullPathToFile, $type = null, $errorCode = 0)
{
    $fs = new Filesystem();

    // Copy the "upload" to a temp file
    $tmpFile = tempnam(sys_get_temp_dir(), "testupload");
    $fs->copy($fullPathToFile, $tmpFile);

    // If we haven't been given it, find the Mime type of a file
    if (!$type) {
        $type = $fs->mimeType($fullPathToFile);
    }

    return new UploadedFile(
        $tmpFile,
        $fs->name($fullPathToFile) . '.' . $fs->extension($fullPathToFile),
        $type,
        $fs->size($tmpFile),
        $errorCode,
        true // $test
    );
}

And Symphony's method that returns the error (also unhelpful...)

/**
 * Returns an informative upload error message.
 *
 * @return string The error message regarding the specified error code
 */
public function getErrorMessage()
{
    static $errors = array(
        UPLOAD_ERR_INI_SIZE => 'The file "%s" exceeds your upload_max_filesize ini directive (limit is %d KiB).',
        UPLOAD_ERR_FORM_SIZE => 'The file "%s" exceeds the upload limit defined in your form.',
        UPLOAD_ERR_PARTIAL => 'The file "%s" was only partially uploaded.',
        UPLOAD_ERR_NO_FILE => 'No file was uploaded.',
        UPLOAD_ERR_CANT_WRITE => 'The file "%s" could not be written on disk.',
        UPLOAD_ERR_NO_TMP_DIR => 'File could not be uploaded: missing temporary directory.',
        UPLOAD_ERR_EXTENSION => 'File upload was stopped by a PHP extension.',
    );

    $errorCode = $this->error;
    $maxFilesize = $errorCode === UPLOAD_ERR_INI_SIZE ? self::getMaxFilesize() / 1024 : 0;
    $message = isset($errors[$errorCode]) ? $errors[$errorCode] : 'The file "%s" was not uploaded due to an unknown error.';

    return sprintf($message, $this->getClientOriginalName(), $maxFilesize);
}

I've confirmed that the file is in /tmp/

-rw------- 1 vagrant vagrant 88 Mar 24 08:53 testuploadA4K2MA

And I've checked it's both read/write enabled. Which it is. I'm completely confused as to why phpunit is failing? Has anyone seen anything like this before? Maybe, please! :)

via Chebli Mohamed