Repair existing snapshots which have erroneously not recorded their author

ContentBit.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;

class ContentBit extends DataObject implements TestOnly
{
    private static $table_name = 'BitOfContent';

    private static $has_one = ['Byte' => ContentByte::class];
}

ContentBitVideo.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;

class ContentBitVideo extends ContentBit implements TestOnly
{
}

ContentByte.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;

class ContentByte extends DataObject implements TestOnly
{
    private static $table_name = 'ByteOfContent';

    private static $has_many = ['Bits' => ContentBit::class];

    private static $owns = ['Bits'];
}

ContentWord.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;

class ContentWord extends DataObject implements TestOnly
{
    private static $table_name = 'WordOfContent';

    private static $has_one = ['Byte' => ContentByte::class];

    private static $owns = ['Byte'];
}

VersionBit.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;
use SilverStripe\Security\Member;

class VersionBit extends DataObject implements TestOnly
{
    private static $table_name = 'BitOfContent_Versions';

    private static $db = [
        'Version' => 'Int',
        'WasPublished' => 'Boolean',
        'WasDeleted' => 'Boolean',
        'WasDraft' => 'Boolean',
    ];

    private static $has_one = [
        'Record' => ContentBit::class,
        'Author' => Member::class,
        'Publisher' => Member::class,
        'Byte' => ContentByte::class,
    ];
}

VersionByte.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;
use SilverStripe\Security\Member;

class VersionByte extends DataObject implements TestOnly
{
    private static $table_name = 'ByteOfContent_Versions';

    private static $db = [
        'Version' => 'Int',
        'WasPublished' => 'Boolean',
        'WasDeleted' => 'Boolean',
        'WasDraft' => 'Boolean',
    ];

    private static $has_one = [
        'Record' => ContentByte::class,
        'Author' => Member::class,
        'Publisher' => Member::class,
    ];
}

VersionedSnapshotsAuthorIntegrityTask.php

<?php

namespace App\Migrations;

use Monolog\Handler\StreamHandler;
use Monolog\Logger;
use Psr\Log\LoggerInterface;
use SilverStripe\Control\Director;
use SilverStripe\Core\Convert;
use SilverStripe\Dev\BuildTask;
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\DB;
use SilverStripe\ORM\Queries\SQLSelect;
use SilverStripe\Snapshots\Snapshot;
use SilverStripe\Snapshots\SnapshotItem;

/**
 * Copies information from ChangeSet records to VersionedSnapshot records to retain CMS visible information after an
 * upgrade. See https://github.com/silverstripe/silverstripe-versioned-snapshot-admin/issues/51
 */
class VersionedSnapshotsAuthorIntegrityTask extends BuildTask
{
    protected $title = 'Ensure an author is correctly set for snapshots used for history auditing';

    protected $description = 'Versioned snapshots used to have a bug where authors were not correctly recorded, as the'
        . ' system relied on the name in the most recent ChangeSet. This task copies the changeset author name across'
        . ' to existing snapshots, as so when the snapshot update to use this data instead of changeset info no data'
        . ' is lost. See https://github.com/silverstripe/silverstripe-versioned-snapshot-admin/issues/51';

    /**
     * @var LoggerInterface
     */
    private $logger;

    private static $segment = 'SnapshotAuthorFix';

    private static $dependencies = [
        'Logger' => '%$' . LoggerInterface::class . '.' . self::class,
    ];

        /**
     * @inheritDoc
     * @codeCoverageIgnore This is (or should be) a run-once-and-delete task
     */
    public function run($request)
    {
        $this->addLogHandlers();

        $totalBad = 0;
        $totalFixed = 0;

        $authorlessSnapshotClasses = $this->getAuthorlessSnapshotDetails();
        $schema = DataObject::getSchema();

        $snapshot = $schema->baseDataTable(Snapshot::class);
        $snapshotId = $schema->sqlColumnForField(Snapshot::class, 'ID');
        $snapshotHash = $schema->sqlColumnForField(Snapshot::class, 'OriginHash');
        $snapshotAuthor = $schema->sqlColumnForField(Snapshot::class, 'AuthorID');
        $snapshotOriginId = $schema->sqlColumnForField(Snapshot::class, 'OriginID');
        $snapshotOriginClass = $schema->sqlColumnForField(Snapshot::class, 'OriginClass');

        $snapshotItem = $schema->baseDataTable(SnapshotItem::class);
        $snapshotItemSnapshot = $schema->sqlColumnForField(SnapshotItem::class, 'SnapshotID');
        $snapshotItemHash = $schema->sqlColumnForField(SnapshotItem::class, 'ObjectHash');
        $snapshotItemVersion = $schema->sqlColumnForField(SnapshotItem::class, 'Version');

        foreach ($authorlessSnapshotClasses as $originClass => $numberBad) {
            $this->report($numberBad . ' snapshots missing authors for ' . $originClass);
            if (!class_exists($originClass)) {
                $this->report(
                    $originClass . ' no longer exists; cannot obtain table information for setting authors',
                    Logger::WARNING
                );

                continue;
            }
            $totalBad += $numberBad;

            // the `_Versions` suffix is hardcoded in {@see Versioned}
            $originVersion = $schema->baseDataTable($originClass) . '_Versions';
            $originVersionVersion = '"' . $originVersion . '"."Version"';
            $originVersionRecordId = '"' . $originVersion . '"."RecordID"';
            $originVersionAuthor = '"' . $originVersion . '"."PublisherID"';

            $rawQueryBecauseSQLUpdateClassDoesNotSupportJoins = 'UPDATE ' . $snapshot . "\n"
                . 'LEFT JOIN ' . $snapshotItem . "\n"
                . ' ON ' . $snapshotId . ' = ' . $snapshotItemSnapshot . "\n"
                . 'LEFT JOIN ' . $originVersion . "\n"
                . ' ON ' . $snapshotOriginId . ' = ' . $originVersionRecordId . "\n"
                . 'SET ' . $snapshotAuthor . ' = ' . $originVersionAuthor . "\n"
                . 'WHERE ' . $snapshotAuthor . " = 0\n"
                . ' AND ' . $originVersionRecordId . " IS NOT NULL\n"
                . ' AND ' . $snapshotHash . ' = ' . $snapshotItemHash . "\n"
                . ' AND ' . $snapshotItemVersion . ' = ' . $originVersionVersion . "\n"
                . ' AND ' . $snapshotOriginClass . " = '" . Convert::raw2sql($originClass) . "'";
            // Luckily there is 0 user input, we're copying already inputted data from one table to another.
            DB::query($rawQueryBecauseSQLUpdateClassDoesNotSupportJoins);

            $updatedRecords = DB::affected_rows();
            $totalFixed += $updatedRecords;
            $remaining = $numberBad - $updatedRecords;
            $this->report(sprintf('Fixed %s - %s malformed records for %s', $updatedRecords, $remaining, $originClass));
        }

        $this->report(sprintf('Fixed %s out of %s malformed records.', $totalFixed, $totalBad));

        if ($totalBad - $totalFixed !== 0) {
            $this->report(
                sprintf(
                    '%s bad records for %s - there could be an undetected bug still logging'
                    . ' snapshots with no author set (this task only fixes `Versioned` initiated actions such as'
                    . ' save/publish), or maybe there was no author (system generated publishes, etc.)',
                    $remaining,
                    $originClass
                ),
                Logger::WARNING
            );
        }
    }

    public function setLogger(LoggerInterface $logger): self
    {
        $this->logger = $logger;

        return $this;
    }

    protected function addLogHandlers()
    {
        $logger = $this->logger;

        if ($logger && Director::is_cli()) {
            $logger->pushHandler(new StreamHandler('php://stdout'));
            $logger->pushHandler(new StreamHandler('php://stderr', Logger::WARNING));
        }
    }

    /**
     * Logs a message
     *
     * @return void
     */
    private function report(string $line, int $level = Logger::NOTICE)
    {
        $logger = $this->logger;
        if (!$logger) {
            return;
        }
        switch ($level) {
            case Logger::WARNING:
                $logger->warning($line);

                break;
            default:
                $logger->notice($line);
        }
    }

    /**
     * Returns list of affected classes (all base class due to nature of Versioned Snapshots) and their affected count
     *
     * @return string[]
     */
    private function getAuthorlessSnapshotDetails()
    {
        $schema = DataObject::getSchema();
        $snapshotTable = $schema->baseDataTable(Snapshot::class);
        $snapshotClassColumn = $schema->sqlColumnForField(Snapshot::class, 'OriginClass');
        $snapshotAuthorColumn = $schema->sqlColumnForField(Snapshot::class, 'AuthorID');
        $authorlessSnapshots = SQLSelect::create(
            [
                'ClassName' => $snapshotClassColumn,
                'Count' => 'count(' . $snapshotClassColumn . ')',
            ],
            $snapshotTable,
            [$snapshotAuthorColumn => 0],
            null,
            $snapshotClassColumn
        );
        $classesToFix = [];
        foreach ($authorlessSnapshots->execute() as $authorlessDetail) {
            $classesToFix[$authorlessDetail['ClassName']] = $authorlessDetail['Count'];
        }

        return $classesToFix;
    }
}

VersionedSnapshotsAuthorIntegrityTaskTest.php

<?php

namespace App\Tests\Migrations;

use App\Migrations\VersionedSnapshotsAuthorIntegrityTask;
use App\Tests\Migrations\Stubs\ContentBit;
use App\Tests\Migrations\Stubs\ContentBitVideo;
use App\Tests\Migrations\Stubs\ContentByte;
use App\Tests\Migrations\Stubs\ContentWord;
use App\Tests\Migrations\Stubs\VersionBit;
use App\Tests\Migrations\Stubs\VersionByte;
use App\Tests\Migrations\Stubs\VersionWord;
use SilverStripe\Control\HTTPRequest;
use SilverStripe\Dev\SapphireTest;
use SilverStripe\Snapshots\Snapshot;
use SilverStripe\Versioned\Versioned;

class VersionedSnapshotsAuthorIntegrityTaskTest extends SapphireTest
{
    protected static $fixture_file = 'VersionedSnapshotsAuthorIntegrityTaskTest.yml';

    protected static $extra_dataobjects = [
        ContentBit::class,
        ContentBitVideo::class,
        ContentByte::class,
        ContentWord::class,
        VersionBit::class,
        VersionByte::class,
        VersionWord::class,
    ];

    protected static $required_extensions = [
        ContentBit::class => [Versioned::class],
        ContentByte::class => [Versioned::class],
        ContentWord::class => [Versioned::class],
    ];

    /**
     * Ensure the task does as it should
     *
     * @return void
     */
    public function testAuthorlessSnapshotsBecomeAuthored()
    {
        $repairTask = new VersionedSnapshotsAuthorIntegrityTask();
        $request = new HTTPRequest('GET', 'dev/tasks/SnapshotAuthorFix');
        $authorlessSnapshots = Snapshot::get()->filter('AuthorID', 0);
        $this->assertSame(6, $authorlessSnapshots->count());
        $repairTask->run($request);
        $this->assertSame(0, $authorlessSnapshots->count());
    }

    /**
     * DataObject writes by default update LastEdited, etc. which would corrupt history auditing in this case.
     *
     * @return void
     */
    public function testDatesOfRepairedSnapshotsAreNotAffected()
    {
        $repairTask = new VersionedSnapshotsAuthorIntegrityTask();
        $request = new HTTPRequest('GET', 'dev/tasks/SnapshotAuthorFix');
        $snapshotDates = Snapshot::get()->column('LastEdited');
        $repairTask->run($request);
        $this->assertSame($snapshotDates, Snapshot::get()->column('LastEdited'));
    }

    /**
     * Ensure we only affect the snapshots we intend to
     *
     * @return void
     */
    public function testAuthorsOfUnaffectedSnapshotsAreNotErroneouslyCorrected()
    {
        $repairTask = new VersionedSnapshotsAuthorIntegrityTask();
        $request = new HTTPRequest('GET', 'dev/tasks/SnapshotAuthorFix');
        $authorlessSnapshotIDs = Snapshot::get()
            ->filter('AuthorID', 0)
            ->column('ID');
        $existingAuthors = Snapshot::get()
            ->exclude('AuthorID', 0)
            ->column('AuthorID');
        $repairTask->run($request);
        $hopefullyUnaffectedExistingAuthors = Snapshot::get()
            ->exclude('ID', $authorlessSnapshotIDs)
            ->column('AuthorID');
        $this->assertSame($existingAuthors, $hopefullyUnaffectedExistingAuthors);
    }
}

VersionedSnapshotsAuthorIntegrityTaskTest.yml

SilverStripe\Security\Member:
  admin:
    FirstName: Site
    Surname: Admin
    email: [email protected]
  author:
    FirstName: Author
    Surname: "O'Content"
    email: [email protected]

App\Tests\Migrations\Stubs\ContentByte:
  area:

App\Tests\Migrations\Stubs\ContentWord:
  page:
    Byte: =>App\Tests\Migrations\Stubs\ContentByte.area

App\Tests\Migrations\Stubs\ContentBit:
  content:
    Byte: =>App\Tests\Migrations\Stubs\ContentByte.area
App\Tests\Migrations\Stubs\ContentBitVideo:
  first:
    Byte: =>App\Tests\Migrations\Stubs\ContentByte.area
  second:
    Byte: =>App\Tests\Migrations\Stubs\ContentByte.area

SilverStripe\Snapshots\Snapshot:
  one:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page
  two:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Author: =>SilverStripe\Security\Member.admin
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  three:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  four:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  five:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Author: =>SilverStripe\Security\Member.admin
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  six:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Author: =>SilverStripe\Security\Member.admin
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  seven:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Author: =>SilverStripe\Security\Member.admin
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page
  eight:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page
  nine:
    OriginHash: 6121a8222606980635054b7dd9daa8c1
    Author: =>SilverStripe\Security\Member.author
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  ten:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Author: =>SilverStripe\Security\Member.author
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page
  eleven:
    OriginHash: 7942bbe24fb5701554459ac4e78f83e3
    Origin: =>App\Tests\Migrations\Stubs\ContentBitVideo.second
  twelve:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page
  thirteen:
    OriginHash: ad671cb0fee3f44de935cd3edbbcfae7
    Author: =>SilverStripe\Security\Member.admin
    Origin: =>App\Tests\Migrations\Stubs\ContentWord.page

SilverStripe\Snapshots\SnapshotItem:
  one:
    Version: 6
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.one
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page
  two:
    Version: 5
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.two
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  three:
    Version: 7
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.three
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  four:
    Version: 9
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.four
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  five:
    Version: 10
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.five
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  six:
    Version: 11
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.six
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  seven:
    Version: 7
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.seven
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page
  eight:
    Version: 8
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.eight
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page
  nine:
    Version: 13
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.nine
    ObjectHash: 6121a8222606980635054b7dd9daa8c1
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
  ten:
    Version: 9
    WasDraft: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.ten
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page
  eleven:
    Version: 6
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.eleven
    ObjectHash: 7942bbe24fb5701554459ac4e78f83e3
    Object: =>App\Tests\Migrations\Stubs\ContentBitVideo.second
  twelve:
    Version: 10
    WasPublished: 1
    Snapshot: =>SilverStripe\Snapshots\Snapshot.twelve
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page
  thirteen:
    Version: 10
    Snapshot: =>SilverStripe\Snapshots\Snapshot.thirteen
    WasDraft: 1
    WasUnpublished: 1
    ObjectHash: ad671cb0fee3f44de935cd3edbbcfae7
    Object: =>App\Tests\Migrations\Stubs\ContentWord.page

App\Tests\Migrations\Stubs\VersionWord:
  one:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 6
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentWord=
  two:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 7
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentWord
  three:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 8
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentWord
  four:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 9
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.author
    ClassName: App\Tests\Migrations\Stubs\ContentWord
  five:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 10
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentWord
  six:
    Record: =>App\Tests\Migrations\Stubs\ContentWord.page
    Version: 10
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentWord

App\Tests\Migrations\Stubs\VersionBit:
  one:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 5
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  two:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 7
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  three:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 9
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    Publisher: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  four:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 10
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  five:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 11
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.admin
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  six:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.first
    Version: 13
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.author
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo
  seven:
    Record: =>App\Tests\Migrations\Stubs\ContentBitVideo.second
    Version: 6
    WasPublished: 1
    WasDraft: 1
    Author: =>SilverStripe\Security\Member.author
    Publisher: =>SilverStripe\Security\Member.author
    ClassName: App\Tests\Migrations\Stubs\ContentBitVideo

VersionWord.php

<?php

namespace App\Tests\Migrations\Stubs;

use SilverStripe\Dev\TestOnly;
use SilverStripe\ORM\DataObject;
use SilverStripe\Security\Member;

class VersionWord extends DataObject implements TestOnly
{
    private static $table_name = 'WordOfContent_Versions';

    private static $db = [
        'Version' => 'Int',
        'WasPublished' => 'Boolean',
        'WasDeleted' => 'Boolean',
        'WasDraft' => 'Boolean',
    ];

    private static $has_one = [
        'Record' => ContentWord::class,
        'Author' => Member::class,
        'Publisher' => Member::class,
        'Byte' => ContentByte::class,
    ];
}

c.f. silverstripe/silverstripe-versioned-snapshots#41

The folder structure was as follows (as hinted by namespaces):

app/src/Migrations
app/tests/Migrations
app/tests/Migraions/Stubs

Where composer.json:

    "autoload": {
        "psr-4": {
            "App\\": "app/src/",
            "App\\Tests\\": "app/tests/"
        }
    },