[5.7] Check that a specific error is missing

[shadoWalker89]

This will allow to check that a specific field has no error in tests.
My use case is the following.

I have a form with these fields

Label, With uploads, Upload label, Upload deadline

The Upload label and Upload deadline fields are only required when the With uploads checkbox is checked.

I have a test where i check that the required field validation is correct.

I'm checking that when the With uploads is not checked i should have no errors for Upload label, Upload deadline

        $response->assertSessionHasErrors(['label']);
        $response->assertSessionHasNoErrors(['presentation_label', 'presentation_upload_deadline']);

Of course this update does not introduce any breaking changes, if the $keys argument is empty we will just assert that there is no errors at all.

Also, i checked the FoundationTestResponseTest and found no existing tests about session error assertions. If you would like i can make another PR to add tests for all session assertions.

[taylorotwell]

Made this a separate method. Made it match corresponding method.