PHP Error: Call to a member function connection() on null in /vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php on line 1344

Question

I'm making my first unit test. For the record, I have coded several functional tests and they work.

Here, there is a little detail, my table measure is hypertable on TimescaleDB ( Postgres ), so I couldn't manage to use migrations / seeds.

Anyway, as it is a unit test, I need no DB connection here.

here is my working config for functional tests:

<php>
        <server name="APP_ENV" value="testing"/>
        <server name="BCRYPT_ROUNDS" value="4"/>
        <server name="CACHE_DRIVER" value="array"/>
        <server name="DB_CONNECTION" value="sqlite"/>
        <server name="DB_DATABASE" value=":memory:"/>
        <server name="MAIL_DRIVER" value="array"/>
        <server name="QUEUE_CONNECTION" value="sync"/>
        <server name="SESSION_DRIVER" value="array"/>
        <env name="TELESCOPE_ENABLED" value="false"/>
    </php>

Here is my code:

 <?php

namespace Tests\Unit;

use App\Measure;
use Carbon\Carbon;
use PHPUnit\Framework\TestCase;

class MeasureTest extends TestCase
{

    public function setUp() : void
    {
        parent::setUp();
    }

    /** @test * */
    public function is_new_timestamp()
    {
        $timestep = "10";
        $targetTimestamp = "30";
        $ts = Carbon::create(2020, 04, 16, 13, 00, 0, null);
        $m1 = new Measure(['time' => $ts]);
        $m2 = new Measure(['time' => (clone $ts)->addMinutes($timestep)]);
        $m3 = new Measure(['time' => (clone $ts)->addMinutes(2 * $timestep)]);
        $m4 = new Measure(['time' => (clone $ts)->addMinutes(3 * $timestep)]);
        $m5 = new Measure(['time' => (clone $ts)->addMinutes(4 * $timestep)]);
        $m6 = new Measure(['time' => (clone $ts)->addMinutes(5 * $timestep)]);

        assertTrue(Measure::isNextTimestamp($m1->time, $targetTimestamp));
        assertFalse(Measure::isNextTimestamp($m2->time, $targetTimestamp));
        assertFalse(Measure::isNextTimestamp($m3->time, $targetTimestamp));

        assertTrue(Measure::isNextTimestamp($m4->time, $targetTimestamp));
        assertFalse(Measure::isNextTimestamp($m5->time, $targetTimestamp));
        assertFalse(Measure::isNextTimestamp($m6->time, $targetTimestamp));
    }

How should I get rid of this error ? Where am i invoking connection() ?