"Solving" the issue of Symfony 3.x and PHPUnit 6.x (obviously this is a hack until they fix it properly)

1_bootstrap.php

<?php

// create a file in /tests/bootstrap.php at the root of your symfony project

$loader = require(__DIR__  . '/../app/autoload.php'); // or whatever path your autoload.php is in
if (!class_exists('\PHPUnit_Framework_TestCase') && class_exists('\PHPUnit\Framework\TestCase')) {
    class_alias('\PHPUnit\Framework\TestCase', '\PHPUnit_Framework_TestCase');
}
return $loader;

// In your phpunit.xml or phpunit.xml.dist change:

         bootstrap="app/autoload.php"

// to
         bootstrap="tests/bootstrap.php"

2_alternative_bootstrap.php

<?php

// Alternatively if you use your own bootstrap file, just add this line:

if (!class_exists('\PHPUnit_Framework_TestCase') && class_exists('\PHPUnit\Framework\TestCase')) {
    class_alias('\PHPUnit\Framework\TestCase', '\PHPUnit_Framework_TestCase');
}

3_hack_composer.php

<?php

// Create a file in /tests/alias.php at the root of your symfony project containing:

if (!class_exists('\PHPUnit_Framework_TestCase') && class_exists('\PHPUnit\Framework\TestCase')) {
    class_alias('\PHPUnit\Framework\TestCase', '\PHPUnit_Framework_TestCase');
}


// In your composer.json We can misuse composer autoloading. 
// much thanks to @WyriHaximus who pointed it out.
// Add the following:

    "autoload-dev": {
        "files": [
            "tests/alias.php"
        ]
    },

Thanks for this. Works really well!

I updated it to support more variants in my Symfony3 project.

$convert = [
    '\PHPUnit_Framework_TestCase' => '\PHPUnit\Framework\TestCase',
    '\PHPUnit_Util_Test' => '\PHPUnit\Util\Test',
    '\PHPUnit_Framework_Constraint' => '\PHPUnit\Framework\Constraint\Constraint',
    '\PHPUnit_Framework_Assert' => '\PHPUnit\Framework\Assert',
    '\PHPUnit_Framework_Constraint_IsEqual' => '\PHPUnit\Framework\Constraint\IsEqual',
    '\PHPUnit_Framework_Constraint_ExceptionMessage' => '\PHPUnit\Framework\Constraint\ExceptionMessage',
];

foreach ($convert as $oldClass => $newClass) {
    if (!class_exists($oldClass) && class_exists($newClass)) {
        class_alias($newClass, $oldClass);
    }
}