Missing columns in database, but only when testing

I have a test which is failing due to a missing column in the database. The weird thing is the column is actually present.

Below is a little test I have run to prove that the column exists.

Controller

public function index()
{
    if (Schema::hasColumn('occurrences', 'occurrenceable_type')) {
        echo 'yes I have the bloody column';
    } else {
        echo 'no column for me!';
    }
}

returns >> 'yes I have the bloody column';

Test

public function an_admin_can_create_a_new_occurrence()
{
    if (Schema::hasColumn('occurrences', 'occurrenceable_type')) {
        echo 'yes I have the bloody column';
    } else {
        echo 'no column for me!';
    }
}

returns >> 'no column for me'

The differences between the test and controller are

Controller: database is a MySQL database connection

Testing: database is a MySQLite database running in memory.

the tests implement use RefreshDatabase; and if a run a artisan migrate:refresh on the MySQL database the column is present.

Why would there be differences between them? How can I solve it?