[7.x] Add assertDatabaseCount assertion

[christophrumpel]

This PR adds a new database assertion called assertDatabaseCount($count).

Next to the given assertDatabaseHas or assertDatabaseMissing assertions, it is often useful to just check the number of entries in a database table. This is possible in different workarounds already, but it would be more convenient to provide a simple helper through Laravel as well.

Here is an example of how to use it inside a test:

MyCustomUserFactory::new()
    ->times(50)
    ->create();

$this->assertDatabaseCount('users', 50);

And this is how a failure message would look like:

Failed asserting that table [products] matches expected entries count of 3. Entries found: 1.

[taylorotwell]

Thanks

[christophrumpel]

👍Do you want it to be added to the docs as well? https://laravel.com/docs/master/database-testing

[veneliniliev]

this is good feature but can you add array $data for additional wheres for count like other assertDatabase* methods?