Laravel extending Illuminate\Foundation\Testing\TestCase with custom namespace

I'm trying to set up unit tests for my Laravel (5.2) API project. Before I use the unit tests I'd like to define a custom namespace for them so I created the namespace Test; in the default TestCase.php file. Like so:

namespace Test;

class TestCase extends Illuminate\Foundation\Testing\TestCase
{
  ...
}

Then I created a folder UnitTests under the tests folder and put my unit tests in that folder with the following namespace:

namespace Test\UnitTests;

use Test\TestCase;

class CreateAccountTest extends TestCase
{
  ...
}

Now when I want to run my unit tests I get the following error:

PHP Fatal error: Class 'Test\Illuminate\Foundation\Testing\TestCase' not found in /var/www/ops/tests/TestCase.php on line 6

So basically, Laravel thinks the Illuminate\Foundation\Testing\TestCaseclass is found within the Test namespace instead of the Illuminatenamespace from Laravel.

I also have the following autoload configured in the composer.json file:

"autoload": {
    "classmap": [
        "database",
        "tests"
    ],
    "psr-4": {
        "App\\": "app/",
        "Test\\": "tests/"
    }
},
"autoload-dev": {
    "classmap": [
        "tests/TestCase.php"
    ]
}

I've also tried running both commands with no success:

• php artisan config:cache
• composer dump-autoload

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