Tests fails with sqlite but works with mysql?

Hi,

I've got a method that looks like this:

protected function saveDescriptions($descriptionsShort, $descriptionsLong, $productId)
{
    /*
     * Check if product description short already exists
     * otherwise create one.
     */

    foreach ($descriptionsShort as $description) {
        if(! ProductDescriptionModel::where(
            'description', $description
        )->where(
            'product_id', $productId
        )->where('type', 'short')->first()) {

            /*
            * If product description short does not exists create one.
            */

            ProductDescriptionModel::create([
                'product_id'    => $productId,
                'description'   => $description,
                'type'          => 'short'
            ]);
        }
    }

This is my test:

 /** @test */
    public function it_creates_product_descriptions_short_correctly()
    {
        $this->assertDatabaseMissing('product_description', [
            "product_id" => 1,
            "description" => "Short description...",
            "type" => "short"
        ]);

        $this->assertDatabaseMissing('product_description', [
            "product_id" => 1,
            "description" => "test",
            "type" => "short"
        ]);

        $this->saveProducts(__dir__ . '/xml/Descriptions.xml');

        $this->assertDatabaseHas('product_description', [
            "product_id" => 1,
            "description" => "Short description...",
            "type" => "short"
        ]);

        $this->assertDatabaseHas('product_description', [
            "product_id" => 1,
            "description" => "test",
            "type" => "short"
        ]);
    }

With this settings in my phpunit.xml file it fails:

<php>
        <env name="APP_ENV" value="testing"/>
        <env name="DB_CONNECTION" value="sqlite" />
        <env name="DB_DATABASE" value=":memory:" />
        <env name="CACHE_DRIVER" value="array"/>
        <env name="SESSION_DRIVER" value="array"/>
        <env name="QUEUE_DRIVER" value="sync"/>
    </php>

but with this it works:

 <php>
        <env name="APP_ENV" value="testing"/>
        <env name="CACHE_DRIVER" value="array"/>
        <env name="SESSION_DRIVER" value="array"/>
        <env name="QUEUE_DRIVER" value="sync"/>
        <env name="DB_DEFAULT" value="sqlite_testing" />
    </php>

What could be the problem? Thanks!