src/HttpAssert.php
public static function assertFetchedToOne(
        $status,
        $contentType,
        $content,
        ?string $type,
        string $id = null,
        string $message = ''
    ): Document
    {
        if (is_null($type) || is_null($id)) {
            return self::assertFetchedNull($status, $contentType, $content, $message);
        }

        return self::assertJsonApi($status, $contentType, $content, self::STATUS_OK, $message)
            ->assertIdentifier($type, $id, '/data', $message);
    }
public static function assertFetchedToOne(
        $status,
        $contentType,
        $content,
        ?string $type,
        string $id = null,
        string $message = ''
    ): Document
    {
        if (is_null($type) || is_null($id)) {
            return self::assertFetchedNull($status, $contentType, $content, $message);
        }

        return self::assertJsonApi($status, $contentType, $content, self::STATUS_OK, $message)
            ->assertIdentifier($type, $id, '/data', $message);
    }
Assert that a to-one relationship was fetched.

If either type or id are null, then it will be asserted that the data member of the content
is null.

@param $status
@param $contentType
@param $content
@param string|null $type
@param string|null $id
@param string $message
@return Document