Better way for testing validation errors

I think there is more clear way to get an exact error message from session.

    /** @var ViewErrorBag $errors */
    $errors = request()->session()->get('errors');
    /** @var array $messages */
    $messages = $errors->getBag('default')->getMessages();
    $emailErrorMessage = array_shift($messages['email']);

    $this->assertEquals('Already in use', $emailErrorMessage);

Pre-requirements: code was tested on Laravel Framework 5.5.14

get the MessageBag object from from session erros and get all the validation error names using $errors->get('name')

    $errors = session('errors');
    $this->assertSessionHasErrors();
    $this->assertEquals($errors->get('name')[0],"The title field is required.");

This works for Laravel 5 +

Your test doesn't have a post call. Here is an example using Jeffery Way's flash package

Controller:

public function store(Request $request, Post $post)
{
    $post->fill($request->all());
    $post->user_id = $request->user()->id;

    $created = false;

    try {
        $created = $post->save();
    } catch (ValidationException $e) {
        flash()->error($e->getErrors()->all());
    }

    if ($created) {
        flash()->success('New post has been created.');
    }

    return back();
}

Test:

public function testStoreSuccess()
{
    $data = [
        'title' => 'A dog is fit',
        'status' => 'active',
        'excerpt' => 'Farm dog',
        'content' => 'blah blah blah',
    ];

    $this->call('POST', 'post', $data);

    $this->assertTrue(Post::where($data)->exists());
    $this->assertResponseStatus(302);
    $this->assertSessionHas('flash_notification.level', 'success');
    $this->assertSessionHas('flash_notification.message', 'New post has been created.');
}

try to split your tests into units, say if you testing a controller function

you may catch valication exception, like so:

} catch (ValidationException $ex) {

if it was generated manually, this is how it should be generated:

throw ValidationException::withMessages([
            'abc' => ['my message'],
        ])->status(400);

you can assert it liks so

$this->assertSame('my message', $ex->errors()['abc'][0]);

if you cannot catch it, but prefer testing routs like so:

    $response = $this->json('POST', route('user-post'), [
        'name'        => $faker->name,
        'email'       => $faker->email,            
    ]);

then you use $response to assert that the validation has happened, like so

$this->assertSame($response->errors->{'name'}[0], 'The name field is required.');

PS

in the example I used

$faker = \Faker\Factory::create();

ValidationException is used liks this

use Illuminate\Validation\ValidationException;

just remind you that you don't have to generate exceptions manually, use validate method for common cases:

$request->validate(['name' => [
            'required',
        ],
    ]);

my current laravel version is 5.7