Unit test for Many to Many Relationship

I'm trying to make sure that my many to many relationship will actually work but what is this error mean?

Failed asserting that Illuminate\Database\Eloquent\Collection Object (...) is an instance of class "App\Role".

My unit test:

$role = factory('App\Role')->create();

$this->assertInstanceOf(User::class, $role->users);

Models:

User

public function roles()
{
    return $this->belongsToMany(Role::class);
}

Role

public function users()
{
    return $this->belongsToMany(User::class);
}

my pivot table:

Schema::create('role_user', function (Blueprint $table) {
        $table->primary(['role_id', 'user_id']);
        $table->unsignedBigInteger('role_id');
        $table->unsignedBigInteger('user_id');
        $table->timestamps();

        $table->foreign('role_id')->references('id')->on('roles')->onDelete('cascade');
        $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
});