diff --git a/php-packages/testing/.editorconfig b/php-packages/testing/.editorconfig
new file mode 100644
index 000000000..a61a3ab36
--- /dev/null
+++ b/php-packages/testing/.editorconfig
@@ -0,0 +1,19 @@
+# EditorConfig helps developers define and maintain consistent
+# coding styles between different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+indent_size = 2
+
+[*.{diff,md}]
+trim_trailing_whitespace = false
+
+[*.{php,xml,json}]
+indent_size = 4
diff --git a/php-packages/testing/.gitattributes b/php-packages/testing/.gitattributes
new file mode 100644
index 000000000..61036520c
--- /dev/null
+++ b/php-packages/testing/.gitattributes
@@ -0,0 +1,15 @@
+.gitattributes export-ignore
+.gitignore export-ignore
+.gitmodules export-ignore
+.github export-ignore
+.travis export-ignore
+.travis.yml export-ignore
+.editorconfig export-ignore
+.styleci.yml export-ignore
+
+phpunit.xml export-ignore
+tests export-ignore
+
+js/dist/* -diff
+
+* text=auto eol=lf
diff --git a/php-packages/testing/.github/workflows/test.yml b/php-packages/testing/.github/workflows/test.yml
new file mode 100644
index 000000000..b7ba28c30
--- /dev/null
+++ b/php-packages/testing/.github/workflows/test.yml
@@ -0,0 +1,83 @@
+name: Tests
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        shell: bash
+        working-directory: tests
+
+    strategy:
+      matrix:
+        php: [7.3, 7.4, '8.0']
+        service: ['mysql:5.7', mariadb]
+        prefix: ['', flarum_]
+
+        include:
+          - service: 'mysql:5.7'
+            db: MySQL
+          - service: mariadb
+            db: MariaDB
+          - prefix: flarum_
+            prefixStr: (prefix)
+
+        exclude:
+          - php: 7.3
+            service: 'mysql:5.7'
+            prefix: flarum_
+          - php: 7.3
+            service: mariadb
+            prefix: flarum_
+          - php: 8.0
+            service: 'mysql:5.7'
+            prefix: flarum_
+          - php: 8.0
+            service: mariadb
+            prefix: flarum_
+
+    services:
+      mysql:
+        image: ${{ matrix.service }}
+        ports:
+          - 13306:3306
+
+    name: 'PHP ${{ matrix.php }} / ${{ matrix.db }} ${{ matrix.prefixStr }}'
+
+    steps:
+      - uses: actions/checkout@master
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: xdebug
+          extensions: curl, dom, gd, json, mbstring, openssl, pdo_mysql, tokenizer, zip
+          tools: phpunit, composer:v2
+
+      # The authentication alter is necessary because newer mysql versions use the `caching_sha2_password` driver,
+      # which isn't supported prior to PHP7.4
+      # When we drop support for PHP7.3, we should remove this from the setup.
+      - name: Create MySQL Database
+        run: |
+          sudo systemctl start mysql
+          mysql -uroot -proot -e 'CREATE DATABASE flarum_test;' --port 13306
+          mysql -uroot -proot -e "ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'root';" --port 13306
+
+      - name: Install Composer dependencies
+        run: composer install
+
+      - name: Setup Composer tests
+        run: composer test:setup
+        env:
+          DB_PORT: 13306
+          DB_PASSWORD: root
+          DB_PREFIX: ${{ matrix.prefix }}
+
+      - name: Run Composer tests
+        run: composer test
+        env:
+          COMPOSER_PROCESS_TIMEOUT: 600
diff --git a/php-packages/testing/.gitignore b/php-packages/testing/.gitignore
new file mode 100644
index 000000000..38a8fa98d
--- /dev/null
+++ b/php-packages/testing/.gitignore
@@ -0,0 +1,10 @@
+/vendor
+composer.lock
+composer.phar
+node_modules
+.DS_Store
+Thumbs.db
+/src/integration/tmp
+.vagrant
+.idea/*
+.vscode
diff --git a/php-packages/testing/.styleci.yml b/php-packages/testing/.styleci.yml
new file mode 100644
index 000000000..5d07e31ea
--- /dev/null
+++ b/php-packages/testing/.styleci.yml
@@ -0,0 +1,18 @@
+preset: recommended
+
+enabled:
+  - logical_not_operators_with_successor_space
+
+disabled:
+  - align_double_arrow
+  - blank_line_after_opening_tag
+  - multiline_array_trailing_comma
+  - new_with_braces
+  - phpdoc_align
+  - phpdoc_order
+  - phpdoc_separation
+  - phpdoc_types
+
+finder:
+  exclude:
+    - "stubs"
diff --git a/php-packages/testing/LICENSE b/php-packages/testing/LICENSE
new file mode 100755
index 000000000..9fe7ef1c7
--- /dev/null
+++ b/php-packages/testing/LICENSE
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2020-2021 Stichting Flarum (Flarum Foundation)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/php-packages/testing/composer.json b/php-packages/testing/composer.json
new file mode 100644
index 000000000..831dcd88c
--- /dev/null
+++ b/php-packages/testing/composer.json
@@ -0,0 +1,33 @@
+{
+    "name": "flarum/testing",
+    "description": "Automated testing infrastructure for Flarum core and extensions.",
+    "keywords": [
+        "forum",
+        "discussion"
+    ],
+    "homepage": "https://flarum.org/",
+    "license": "MIT",
+    "require": {
+        "ext-json": "*",
+        "mockery/mockery": "^1.4",
+        "phpunit/phpunit": "^9.0"
+    },
+    "require-dev": {
+        "flarum/core": "*@dev"
+    },
+    "autoload": {
+        "psr-4": {
+            "Flarum\\Testing\\": "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Flarum\\Testing\\Tests\\": "src/tests/"
+        }
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-master": "1.x-dev"
+        }
+    }
+}
diff --git a/php-packages/testing/src/integration/BuildsHttpRequests.php b/php-packages/testing/src/integration/BuildsHttpRequests.php
new file mode 100644
index 000000000..6b379702a
--- /dev/null
+++ b/php-packages/testing/src/integration/BuildsHttpRequests.php
@@ -0,0 +1,69 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration;
+
+use Carbon\Carbon;
+use Dflydev\FigCookies\SetCookie;
+use Illuminate\Support\Str;
+use Laminas\Diactoros\CallbackStream;
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+
+/**
+ * A collection of helpers for building PSR-7 requests for integration tests.
+ */
+trait BuildsHttpRequests
+{
+    protected function requestWithJsonBody(Request $req, array $json): Request
+    {
+        return $req
+            ->withHeader('Content-Type', 'application/json')
+            ->withBody(
+                new CallbackStream(function () use ($json) {
+                    return json_encode($json);
+                })
+            );
+    }
+
+    protected function requestAsUser(Request $req, int $userId): Request
+    {
+        $token = Str::random(40);
+
+        /**
+         * We insert this directly instead of via `prepareDatabase`
+         * so that requests can be created/sent after the app is booted.
+         */
+        $this->database()->table('access_tokens')->insert([
+            'token' => $token,
+            'user_id' => $userId,
+            'created_at' => Carbon::now()->toDateTimeString(),
+            'last_activity_at' => Carbon::now()->toDateTimeString(),
+            'type' => 'session'
+        ]);
+
+        return $req->withAddedHeader('Authorization', "Token {$token}");
+    }
+
+    protected function requestWithCookiesFrom(Request $req, Response $previous): Request
+    {
+        $cookies = array_reduce(
+            $previous->getHeader('Set-Cookie'),
+            function ($memo, $setCookieString) {
+                $setCookie = SetCookie::fromSetCookieString($setCookieString);
+                $memo[$setCookie->getName()] = $setCookie->getValue();
+
+                return $memo;
+            },
+            []
+        );
+
+        return $req->withCookieParams($cookies);
+    }
+}
diff --git a/php-packages/testing/src/integration/ConsoleTestCase.php b/php-packages/testing/src/integration/ConsoleTestCase.php
new file mode 100644
index 000000000..a29db0895
--- /dev/null
+++ b/php-packages/testing/src/integration/ConsoleTestCase.php
@@ -0,0 +1,44 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration;
+
+use Flarum\Foundation\Application;
+use Symfony\Component\Console\Application as ConsoleApplication;
+use Symfony\Component\Console\Input\ArrayInput;
+use Symfony\Component\Console\Output\BufferedOutput;
+
+abstract class ConsoleTestCase extends TestCase
+{
+    protected $console;
+
+    protected function console()
+    {
+        if (is_null($this->console)) {
+            $this->console = new ConsoleApplication('Flarum', Application::VERSION);
+            $this->console->setAutoExit(false);
+
+            foreach ($this->app()->getConsoleCommands() as $command) {
+                $this->console->add($command);
+            }
+        }
+
+        return $this->console;
+    }
+
+    protected function runCommand(array $inputArray)
+    {
+        $input = new ArrayInput($inputArray);
+        $output = new BufferedOutput();
+
+        $this->console()->run($input, $output);
+
+        return trim($output->fetch());
+    }
+}
diff --git a/php-packages/testing/src/integration/Extend/BeginTransactionAndSetDatabase.php b/php-packages/testing/src/integration/Extend/BeginTransactionAndSetDatabase.php
new file mode 100644
index 000000000..cc088686f
--- /dev/null
+++ b/php-packages/testing/src/integration/Extend/BeginTransactionAndSetDatabase.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace Flarum\Testing\integration\Extend;
+
+use Flarum\Extend\ExtenderInterface;
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+use Illuminate\Database\ConnectionInterface;
+
+class BeginTransactionAndSetDatabase implements ExtenderInterface
+{
+    /**
+     * A callback to set the database connection object on the test case.
+     */
+    protected $setDbOnTestCase;
+
+    public function __construct(callable $setDbOnTestCase)
+    {
+        $this->setDbOnTestCase = $setDbOnTestCase;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $db = $container->make(ConnectionInterface::class);
+
+        $db->beginTransaction();
+
+        ($this->setDbOnTestCase)($db);
+    }
+}
diff --git a/php-packages/testing/src/integration/Extend/OverrideExtensionManagerForTests.php b/php-packages/testing/src/integration/Extend/OverrideExtensionManagerForTests.php
new file mode 100644
index 000000000..8d66e7319
--- /dev/null
+++ b/php-packages/testing/src/integration/Extend/OverrideExtensionManagerForTests.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Flarum\Testing\integration\Extend;
+
+use Flarum\Extend\ExtenderInterface;
+use Flarum\Extension\Extension;
+use Flarum\Extension\ExtensionManager;
+use Flarum\Testing\integration\Extension\ExtensionManagerIncludeCurrent;
+use Illuminate\Contracts\Container\Container;
+
+class OverrideExtensionManagerForTests implements ExtenderInterface
+{
+    /**
+     * IDs of extensions to boot
+     */
+    protected $extensions;
+
+    public function __construct($extensions)
+    {
+        $this->extensions = $extensions;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $container->when(ExtensionManagerIncludeCurrent::class)->needs('$enabledIds')->give($this->extensions);
+        if (count($this->extensions)) {
+            $container->singleton(ExtensionManager::class, ExtensionManagerIncludeCurrent::class);
+            $extensionManager = $container->make(ExtensionManager::class);
+
+            foreach ($this->extensions as $extension) {
+                $extensionManager->enable($extension);
+            }
+
+            $extensionManager->booted = true;
+
+            $extensionManager->extend($container);
+        }
+    }
+}
diff --git a/php-packages/testing/src/integration/Extend/SetSettingsBeforeBoot.php b/php-packages/testing/src/integration/Extend/SetSettingsBeforeBoot.php
new file mode 100644
index 000000000..51957b19a
--- /dev/null
+++ b/php-packages/testing/src/integration/Extend/SetSettingsBeforeBoot.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Flarum\Testing\integration\Extend;
+
+use Flarum\Extend\ExtenderInterface;
+use Flarum\Extension\Extension;
+use Flarum\Settings\SettingsRepositoryInterface;
+use Illuminate\Contracts\Container\Container;
+
+class SetSettingsBeforeBoot implements ExtenderInterface
+{
+    /**
+     * IDs of extensions to boot
+     */
+    protected $settings;
+
+    public function __construct($settings)
+    {
+        $this->settings = $settings;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        if (count($this->settings)) {
+            $settings = $container->make(SettingsRepositoryInterface::class);
+            
+            foreach ($this->settings as $key => $value) {
+                $settings->set($key, $value);
+            }
+        }
+    }
+}
diff --git a/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php b/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php
new file mode 100644
index 000000000..1a3dbc8f0
--- /dev/null
+++ b/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php
@@ -0,0 +1,113 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration\Extension;
+
+use Flarum\Database\Migrator;
+use Flarum\Extension\Extension;
+use Flarum\Extension\ExtensionManager;
+use Flarum\Foundation\Paths;
+use Flarum\Settings\SettingsRepositoryInterface;
+use Illuminate\Contracts\Container\Container;
+use Illuminate\Contracts\Events\Dispatcher;
+use Illuminate\Contracts\Filesystem\Cloud;
+use Illuminate\Filesystem\Filesystem;
+use Illuminate\Filesystem\FilesystemAdapter;
+use Illuminate\Support\Arr;
+use League\Flysystem\Adapter\Local;
+use League\Flysystem\Filesystem as FlysystemFilesystem;
+
+class ExtensionManagerIncludeCurrent extends ExtensionManager
+{
+    /**
+     * @var array
+     */
+    protected $enabledIds;
+
+    /**
+     * @var bool
+     */
+    public $booted = false;
+
+    public function __construct(
+        SettingsRepositoryInterface $config,
+        Paths $paths,
+        Container $container,
+        Migrator $migrator,
+        Dispatcher $dispatcher,
+        Filesystem $filesystem,
+        array $enabledIds
+    ) {
+        parent::__construct($config, $paths, $container, $migrator, $dispatcher, $filesystem);
+
+        $this->enabledIds = $enabledIds;
+    }
+
+    /**
+     * @{@inheritDoc}
+     */
+    public function getExtensions()
+    {
+        $extensions = parent::getExtensions();
+
+        $package = json_decode($this->filesystem->get($this->paths->vendor . '/../composer.json'), true);
+
+        if (Arr::get($package, 'type') === 'flarum-extension') {
+            $current = new Extension($this->paths->vendor . '/../', $package);
+            $current->setInstalled(true);
+            $current->setVersion(Arr::get($package, 'version'));
+            $current->calculateDependencies([], []);
+
+            $extensions->put($current->getId(), $current);
+
+            $this->extensions = $extensions->sortBy(function ($extension, $name) {
+                return $extension->composerJsonAttribute('extra.flarum-extension.title');
+            });
+        }
+
+        return $this->extensions;
+    }
+
+    /**
+     * We assume it's not enabled during boot.
+     * However, since some logic needs this, as soon as we enable extensions
+     * we'll switch booted to on.
+     */
+    public function isEnabled($extension)
+    {
+        if (!$this->booted) return false;
+
+        return parent::isEnabled($extension);
+    }
+
+    /**
+     * In test cases, enabled extensions are determined by the test case, not the database.
+     */
+    public function getEnabled()
+    {
+        return $this->enabledIds;
+    }
+
+    /**
+     * Enabled extensions must be specified by the test case, so this should do nothing.
+     */
+    protected function setEnabledExtensions(array $enabledExtensions)
+    {
+    }
+
+    /**
+     * Get an instance of the assets filesystem.
+     * This is resolved dynamically because Flarum's filesystem configuration
+     * might not be booted yet when the ExtensionManager singleton initializes.
+     */
+    protected function getAssetsFilesystem(): Cloud
+    {
+        return new FilesystemAdapter(new FlysystemFilesystem(new Local($this->paths->public . '/assets'), ['url' => resolve('flarum.config')->url() . '/assets']));
+    }
+}
diff --git a/php-packages/testing/src/integration/RetrievesAuthorizedUsers.php b/php-packages/testing/src/integration/RetrievesAuthorizedUsers.php
new file mode 100644
index 000000000..8eefc75f6
--- /dev/null
+++ b/php-packages/testing/src/integration/RetrievesAuthorizedUsers.php
@@ -0,0 +1,24 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration;
+
+trait RetrievesAuthorizedUsers
+{
+    protected function normalUser(): array
+    {
+        return [
+            'id' => 2,
+            'username' => 'normal',
+            'password' => '$2y$10$LO59tiT7uggl6Oe23o/O6.utnF6ipngYjvMvaxo1TciKqBttDNKim', // BCrypt hash for "too-obscure"
+            'email' => 'normal@machine.local',
+            'is_email_confirmed' => 1,
+        ];
+    }
+}
diff --git a/php-packages/testing/src/integration/Setup/SetupScript.php b/php-packages/testing/src/integration/Setup/SetupScript.php
new file mode 100644
index 000000000..0767db596
--- /dev/null
+++ b/php-packages/testing/src/integration/Setup/SetupScript.php
@@ -0,0 +1,149 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration\Setup;
+
+use Flarum\Foundation\Paths;
+use Flarum\Install\AdminUser;
+use Flarum\Install\BaseUrl;
+use Flarum\Install\DatabaseConfig;
+use Flarum\Install\Installation;
+use Flarum\Install\Steps\ConnectToDatabase;
+use Flarum\Testing\integration\UsesTmpDir;
+
+class SetupScript
+{
+    use UsesTmpDir;
+
+    /**
+     * Test database host.
+     *
+     * @var string
+     */
+    protected $host;
+
+    /**
+     * Test database port.
+     *
+     * @var int
+     */
+    protected $port;
+
+    /**
+     * Test database name.
+     *
+     * @var string
+     */
+    protected $name;
+
+    /**
+     * Test database username.
+     *
+     * @var string
+     */
+    protected $user;
+
+    /**
+     * Test database password.
+     *
+     * @var string
+     */
+    protected $pass;
+
+    /**
+     * Test database prefix.
+     *
+     * @var string
+     */
+    protected $pref;
+
+    /**
+     * @var DatabaseConfig
+     */
+    private $dbConfig;
+
+    public function __construct()
+    {
+        $this->host = getenv('DB_HOST') ?: 'localhost';
+        $this->port = intval(getenv('DB_PORT') ?: 3306);
+        $this->name = getenv('DB_DATABASE') ?: 'flarum_test';
+        $this->user = getenv('DB_USERNAME') ?: 'root';
+        $this->pass = getenv('DB_PASSWORD') ?? 'root';
+        $this->pref = getenv('DB_PREFIX') ?: '';
+    }
+
+    public function run()
+    {
+        $tmp = $this->tmpDir();
+
+        echo "Connecting to database $this->name at $this->host:$this->port.\n";
+        echo "Warning: all tables will be dropped to ensure clean state. DO NOT use your production database!\n";
+        echo "Logging in as $this->user with password '$this->pass'.\n";
+        echo "Table prefix: '$this->pref'\n";
+        echo "\nStoring test config in '$tmp'\n";
+
+        echo "\n\nCancel now if that's not what you want...\n";
+        echo "Use the following environment variables for configuration:\n";
+        echo "Database: DB_HOST, DB_PORT, DB_DATABASE, DB_USERNAME, DB_PASSWORD, DB_PREFIX\n";
+        echo "Test Config: FLARUM_TEST_TMP_DIR or FLARUM_TEST_TMP_DIR_LOCAL\n";
+
+
+        sleep(4);
+
+        echo "\nOff we go...\n";
+
+        $this->dbConfig = new DatabaseConfig('mysql', $this->host, $this->port, $this->name, $this->user, $this->pass, $this->pref);
+
+        echo "\nWiping DB to ensure clean state\n";
+        $this->wipeDb();
+        echo "Success! Proceeding to installation...\n";
+
+        $this->setupTmpDir();
+
+        $installation = new Installation(
+            new Paths([
+                'base' => $tmp,
+                'public' => "$tmp/public",
+                'storage' => "$tmp/storage",
+                'vendor' => getcwd() . '/vendor',
+            ])
+        );
+
+        $pipeline = $installation
+            ->configPath('config.php')
+            ->debugMode(true)
+            ->baseUrl(BaseUrl::fromString('http://localhost'))
+            ->databaseConfig($this->dbConfig)
+            ->adminUser(new AdminUser(
+                'admin',
+                'password',
+                'admin@machine.local'
+            ))
+            ->settings(['mail_driver' => 'log'])
+            ->extensions([])
+            ->build();
+
+        // Run the actual configuration
+        $pipeline->run();
+
+        echo "Installation complete\n";
+    }
+
+    protected function wipeDb()
+    {
+        // Reuse the connection step to include version checks
+        (new ConnectToDatabase($this->dbConfig, function ($db) {
+            // Inspired by Laravel's db:wipe
+            $builder = $db->getSchemaBuilder();
+
+            $builder->dropAllTables();
+            $builder->dropAllViews();
+        }))->run();
+    }
+}
diff --git a/php-packages/testing/src/integration/TestCase.php b/php-packages/testing/src/integration/TestCase.php
new file mode 100644
index 000000000..034db0f3f
--- /dev/null
+++ b/php-packages/testing/src/integration/TestCase.php
@@ -0,0 +1,295 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\integration;
+
+use Flarum\Extend\ExtenderInterface;
+use Flarum\Foundation\Config;
+use Flarum\Foundation\InstalledSite;
+use Flarum\Foundation\Paths;
+use Flarum\Testing\integration\Extend\BeginTransactionAndSetDatabase;
+use Flarum\Testing\integration\Extend\OverrideExtensionManagerForTests;
+use Flarum\Testing\integration\Extend\SetSettingsBeforeBoot;
+use Illuminate\Database\ConnectionInterface;
+use Illuminate\Support\Arr;
+use Laminas\Diactoros\ServerRequest;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+abstract class TestCase extends \PHPUnit\Framework\TestCase
+{
+    use BuildsHttpRequests;
+    use UsesTmpDir;
+
+    /**
+     * @inheritDoc
+     */
+    protected function tearDown(): void
+    {
+        parent::tearDown();
+
+        $this->database()->rollBack();
+    }
+
+    /**
+     * @var \Flarum\Foundation\InstalledApp
+     */
+    protected $app;
+
+    /**
+     * @return \Flarum\Foundation\InstalledApp
+     */
+    protected function app()
+    {
+        if (is_null($this->app)) {
+            $tmp = $this->tmpDir();
+
+            $config = include "$tmp/config.php";
+
+            foreach ($this->config as $key => $value) {
+                Arr::set($config, $key, $value);
+            }
+
+            $site = new InstalledSite(
+                new Paths([
+                    'base' => $tmp,
+                    'public' => "$tmp/public",
+                    'storage' => "$tmp/storage",
+                    'vendor' => getcwd().'/vendor',
+                ]),
+                new Config($config)
+            );
+
+            $extenders = array_merge([
+                new OverrideExtensionManagerForTests($this->extensions),
+                new BeginTransactionAndSetDatabase(function (ConnectionInterface $db) {
+                    $this->database = $db;
+                }),
+                new SetSettingsBeforeBoot($this->settings),
+            ], $this->extenders);
+
+            $site->extendWith($extenders);
+
+            $this->app = $site->bootApp();
+
+            $this->populateDatabase();
+        }
+
+        return $this->app;
+    }
+
+    /**
+     * @var ExtenderInterface[]
+     */
+    protected $extenders = [];
+
+    /**
+     * Each argument should be an instance of an extender that should
+     * be applied at application boot.
+     * 
+     * Note that this method will have no effect if called after the
+     * application is booted.
+     */
+    protected function extend(ExtenderInterface ...$extenders)
+    {
+        $this->extenders = array_merge($this->extenders, $extenders);
+    }
+
+    /**
+     * @var string[]
+     */
+    protected $extensions = [];
+
+    /**
+     * Each argument should be an ID of an extension to be enabled.
+     * Extensions other than the one currently being tested must be
+     * listed in this extension's `composer.json` under `require` or
+     * `require-dev`.
+     * 
+     * Note that this method will have no effect if called after the
+     * application is booted.
+     */
+    protected function extension(string ...$extensions)
+    {
+        $this->extensions = array_merge($this->extensions, $extensions);
+    }
+
+    /**
+     * @var array
+     */
+    protected $config = [];
+
+    /**
+     * Some Flarum code depends on config.php values. Flarum doesn't
+     * offer a way to set them at runtime, so this method lets you
+     * add/override them before boot.
+     * 
+     * You can use dot-separated syntax to assign values to subarrays.
+     * 
+     * For example:
+     * 
+     * `$this->config('a.b.c', 'value');` will result in the following:
+     * 
+     * [
+     *     'a' => [
+     *         'b' => ['c' => 'value']
+     *     ]
+     * ]
+     * 
+     * Note that this method will have no effect if called after the
+     * application is booted.
+     */
+    protected function config(string $key, $value)
+    {
+        $this->config[$key] = $value;
+    }
+
+    /**
+     * @var array
+     */
+    protected $settings = [];
+
+    /**
+     * Some settings are used during application boot, so setting
+     * them via `prepareDatabase` will be too late for the desired
+     * effect. For instance, in core the active display name driver
+     * is configured based on the `display_name_driver` setting.
+     * That setting should be registered using this method.
+     * 
+     * Note that this method will have no effect if called after the
+     * application is booted.
+     */
+    protected function setting(string $key, $value)
+    {
+        $this->settings[$key] = $value;
+    }
+
+    /**
+     * @var RequestHandlerInterface
+     */
+    protected $server;
+
+    protected function server(): RequestHandlerInterface
+    {
+        if (is_null($this->server)) {
+            $this->server = $this->app()->getRequestHandler();
+        }
+
+        return $this->server;
+    }
+
+    protected $database;
+
+    protected function database(): ConnectionInterface
+    {
+        $this->app();
+        // Set in `BeginTransactionAndSetDatabase` extender.
+        return $this->database;
+    }
+
+    protected $databaseContent = [];
+
+    protected function prepareDatabase(array $tableData)
+    {
+        $this->databaseContent = array_merge_recursive(
+            $this->databaseContent,
+            $tableData
+        );
+    }
+
+    protected function populateDatabase()
+    {
+        // We temporarily disable foreign key checks to simplify this process.
+        $this->database()->getSchemaBuilder()->disableForeignKeyConstraints();
+
+        // Then, insert all rows required for this test case.
+        foreach ($this->databaseContent as $table => $rows) {
+            foreach ($rows as $row) {
+                if ($table === 'settings') {
+                    $this->database()->table($table)->updateOrInsert(
+                        ['key' => $row['key']],
+                        $row
+                    );
+                } else {
+                    $this->database()->table($table)->updateOrInsert(
+                        isset($row['id']) ? ['id' => $row['id']] : $row,
+                        $row
+                    );
+                }
+            }
+        }
+
+        // And finally, turn on foreign key checks again.
+        $this->database()->getSchemaBuilder()->enableForeignKeyConstraints();
+    }
+
+    /**
+     * Send a full HTTP request through Flarum's middleware stack.
+     */
+    protected function send(ServerRequestInterface $request): ResponseInterface
+    {
+        return $this->server()->handle($request);
+    }
+
+    /**
+     * Build a HTTP request that can be passed through middleware.
+     *
+     * This method simplifies building HTTP requests for use in our HTTP-level
+     * integration tests. It provides options for all features repeatedly being
+     * used in those tests.
+     *
+     * @param string $method
+     * @param string $path
+     * @param array $options
+     *   An array of optional request properties.
+     *   Currently supported:
+     *   - "json" should point to a JSON-serializable object that will be
+     *     serialized and used as request body. The corresponding Content-Type
+     *     header will be set automatically.
+     *   - "authenticatedAs" should identify an *existing* user by ID. This will
+     *     cause an access token to be created for this user, which will be used
+     *     to authenticate the request via the "Authorization" header.
+     *   - "cookiesFrom" should hold a response object from a previous HTTP
+     *     interaction. All cookies returned from the server in that response
+     *     (via the "Set-Cookie" header) will be copied to the cookie params of
+     *     the new request.
+     * @return ServerRequestInterface
+     */
+    protected function request(string $method, string $path, array $options = []): ServerRequestInterface
+    {
+        $request = new ServerRequest([], [], $path, $method);
+
+        // Do we want a JSON request body?
+        if (isset($options['json'])) {
+            $request = $this->requestWithJsonBody(
+                $request,
+                $options['json']
+            );
+        }
+
+        // Authenticate as a given user
+        if (isset($options['authenticatedAs'])) {
+            $request = $this->requestAsUser(
+                $request,
+                $options['authenticatedAs']
+            );
+        }
+
+        // Let's copy the cookies from a previous response
+        if (isset($options['cookiesFrom'])) {
+            $request = $this->requestWithCookiesFrom(
+                $request,
+                $options['cookiesFrom']
+            );
+        }
+
+        return $request;
+    }
+}
diff --git a/php-packages/testing/src/integration/UsesTmpDir.php b/php-packages/testing/src/integration/UsesTmpDir.php
new file mode 100644
index 000000000..23f2eb279
--- /dev/null
+++ b/php-packages/testing/src/integration/UsesTmpDir.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Flarum\Testing\integration;
+
+trait UsesTmpDir
+{
+    public function tmpDir() {
+        return getenv('FLARUM_TEST_TMP_DIR_LOCAL') ?: getenv('FLARUM_TEST_TMP_DIR') ?: __DIR__.'/tmp';
+    }
+
+    public function setupTmpDir() {
+        $DIRS_NEEDED = [
+            '/',
+            '/public',
+            '/public/assets',
+            '/storage',
+            '/storage/formatter',
+            '/storage/sessions',
+            '/storage/views',
+            '/vendor',
+            '/vendor/composer'
+        ];
+
+        $FILES_NEEDED = [
+            '/vendor/composer/installed.json' => '{}'
+        ];
+
+        $tmpDir = $this->tmpDir();
+
+        foreach ($DIRS_NEEDED as $path) {
+            $fullPath = $tmpDir.$path;
+            if (!file_exists($fullPath)) {
+                mkdir($fullPath);
+            }
+        }
+
+        foreach ($FILES_NEEDED as $path => $contents) {
+            $fullPath = $tmpDir.$path;
+            if (!file_exists($fullPath)) {
+                file_put_contents($fullPath, $contents);
+            }
+        }
+    }
+}
diff --git a/php-packages/testing/src/unit/TestCase.php b/php-packages/testing/src/unit/TestCase.php
new file mode 100644
index 000000000..ae04b4cac
--- /dev/null
+++ b/php-packages/testing/src/unit/TestCase.php
@@ -0,0 +1,18 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\unit;
+
+use Mockery\Adapter\Phpunit\MockeryPHPUnitIntegration;
+
+abstract class TestCase extends \PHPUnit\Framework\TestCase
+{
+    // Ensure Mockery is always torn down automatically after each test.
+    use MockeryPHPUnitIntegration;
+}
diff --git a/php-packages/testing/tests/.gitignore b/php-packages/testing/tests/.gitignore
new file mode 100644
index 000000000..208a59913
--- /dev/null
+++ b/php-packages/testing/tests/.gitignore
@@ -0,0 +1 @@
+vendor/*
\ No newline at end of file
diff --git a/php-packages/testing/tests/README.md b/php-packages/testing/tests/README.md
new file mode 100644
index 000000000..ec93c967f
--- /dev/null
+++ b/php-packages/testing/tests/README.md
@@ -0,0 +1 @@
+A minimal extension skeleton to test the flarum/testing package.
\ No newline at end of file
diff --git a/php-packages/testing/tests/composer.json b/php-packages/testing/tests/composer.json
new file mode 100644
index 000000000..cc8ba7bb9
--- /dev/null
+++ b/php-packages/testing/tests/composer.json
@@ -0,0 +1,35 @@
+{
+  "name": "flarum/testing-tests",
+  "description": "Minimal extension to test the flarum/testing package",
+  "type": "flarum-extension",
+  "require": {
+    "flarum/core": "^0.1.0@dev"
+  },
+  "require-dev": {
+    "flarum/testing": "*@dev"
+  },
+  "autoload-dev": {
+    "psr-4": {
+      "Flarum\\Testing\\Tests\\": "tests/"
+    }
+  },
+  "scripts": {
+    "test": [
+      "@test:unit",
+      "@test:integration"
+    ],
+    "test:unit": "phpunit -c tests/phpunit.unit.xml",
+    "test:integration": "phpunit -c tests/phpunit.integration.xml",
+    "test:setup": "@php tests/integration/setup.php"
+  },
+  "scripts-descriptions": {
+    "test": "Runs all tests.",
+    "test:unit": "Runs all unit tests.",
+    "test:integration": "Runs all integration tests.",
+    "test:setup": "Sets up a database for use with integration tests. Execute this only once."
+  },
+  "repositories": [{
+      "type": "path",
+      "url": "../"
+    }]
+}
diff --git a/php-packages/testing/tests/extend.php b/php-packages/testing/tests/extend.php
new file mode 100644
index 000000000..9c49c556f
--- /dev/null
+++ b/php-packages/testing/tests/extend.php
@@ -0,0 +1,19 @@
+<?php
+
+/*
+ * This file is part of flarum/testing-tests.
+ *
+ * Copyright (c) 2021 .
+ *
+ * For the full copyright and license information, please view the LICENSE.md
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing;
+
+use Flarum\Extend;
+
+return [
+    (new Extend\Settings)->serializeToForum('notARealSetting', 'not.a.real.setting'),
+    (new Extend\Frontend('forum'))->route('/added-by-extension', 'added-by-extension')
+];
diff --git a/php-packages/testing/tests/migrations/2021_05_11_000000_create_table_so_we_can_check_existence.php b/php-packages/testing/tests/migrations/2021_05_11_000000_create_table_so_we_can_check_existence.php
new file mode 100644
index 000000000..649dff1b9
--- /dev/null
+++ b/php-packages/testing/tests/migrations/2021_05_11_000000_create_table_so_we_can_check_existence.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Flarum\Testing;
+
+use Flarum\Database\Migration;
+use Illuminate\Database\Schema\Blueprint;
+
+return Migration::createTable('testing_table', function (Blueprint $table) {
+    $table->string('id', 100)->primary();
+});
\ No newline at end of file
diff --git a/php-packages/testing/tests/tests/.phpunit.result.cache b/php-packages/testing/tests/tests/.phpunit.result.cache
new file mode 100644
index 000000000..05fbec964
--- /dev/null
+++ b/php-packages/testing/tests/tests/.phpunit.result.cache
@@ -0,0 +1 @@
+C:37:"PHPUnit\Runner\DefaultTestResultCache":219:{a:2:{s:7:"defects";a:1:{s:74:"Flarum\Testing\Tests\integration\TestCaseTest::can_add_settings_via_method";i:4;}s:5:"times";a:1:{s:74:"Flarum\Testing\Tests\integration\TestCaseTest::can_add_settings_via_method";d:0.09;}}}
\ No newline at end of file
diff --git a/php-packages/testing/tests/tests/fixtures/.gitkeep b/php-packages/testing/tests/tests/fixtures/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/php-packages/testing/tests/tests/integration/TestCaseTest.php b/php-packages/testing/tests/tests/integration/TestCaseTest.php
new file mode 100644
index 000000000..2b7c3814e
--- /dev/null
+++ b/php-packages/testing/tests/tests/integration/TestCaseTest.php
@@ -0,0 +1,211 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Testing\Tests\integration;
+
+use Flarum\Extend;
+use Flarum\Foundation\Config;
+use Flarum\Settings\SettingsRepositoryInterface;
+use Flarum\Testing\integration\TestCase;
+use Flarum\User\User;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Schema\Builder;
+
+class TestCaseTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function admin_user_created_as_part_of_default_state()
+    {
+        $this->app();
+
+        $this->assertEquals(1, User::query()->count());
+    
+        $user = User::find(1);
+
+        $this->assertEquals('admin', $user->username);
+        $this->assertEquals('admin@machine.local', $user->email);
+        $this->assertTrue($user->isAdmin());
+    }
+
+    /**
+     * @test
+     */
+    public function can_add_settings_via_method()
+    {
+        $this->setting('hello', 'world');
+        $this->setting('display_name_driver', 'something_other_than_username');
+
+        $settings = $this->app()->getContainer()->make(SettingsRepositoryInterface::class);
+
+        $this->assertEquals('world', $settings->get('hello'));
+        $this->assertEquals('something_other_than_username', $settings->get('display_name_driver'));
+    }
+
+    /**
+     * @test
+     */
+    public function settings_cleaned_up_from_previous_method()
+    {
+        $settings = $this->app()->getContainer()->make(SettingsRepositoryInterface::class);
+
+        $this->assertEquals(null, $settings->get('hello'));
+        $this->assertEquals(null, $settings->get('display_name_driver'));
+    }
+
+    /**
+     * @test
+     */
+    public function can_add_config_via_method()
+    {
+        $this->config('hello', 'world');
+        $this->config('url', 'https://flarum.org');
+        $this->config('level1.level2', 'value');
+
+        $config = $this->app()->getContainer()->make(Config::class);
+
+        $this->assertEquals('world', $config['hello']);
+        $this->assertEquals('https://flarum.org', $config['url']);
+        $this->assertEquals('value', $config['level1']['level2']);
+    }
+
+    /**
+     * @test
+     */
+    public function config_cleaned_up_from_previous_method()
+    {
+        $config = $this->app()->getContainer()->make(Config::class);
+
+        $this->assertEquals(null, $config['hello']);
+        $this->assertEquals('http://localhost', $config['url']);
+        $this->assertFalse(isset($config['level1']['level2']));
+    }
+
+    /**
+     * @test
+     */
+    public function current_extension_not_applied_by_default()
+    {
+        $response = $this->send(
+            $this->request('GET', '/')
+        );
+
+        $this->assertStringNotContainsString('notARealSetting', $response->getBody()->getContents());
+    }
+
+    /**
+     * @test
+     */
+    public function current_extension_applied_if_specified()
+    {
+        $this->extension('flarum-testing-tests');
+
+        $response = $this->send(
+            $this->request('GET', '/')
+        );
+
+        $this->assertStringContainsString('notARealSetting', $response->getBody()->getContents());
+    }
+
+    /**
+     * @test
+     */
+    public function current_extension_migrations_applied_if_specified()
+    {
+        $this->extension('flarum-testing-tests');
+
+        $tableExists = $this->app()->getContainer()->make(Builder::class)->hasTable('testing_table');
+        $this->assertTrue($tableExists);
+    }
+
+    /**
+     * @test
+     */
+    public function current_extension_considered_enabled_after_boot()
+    {
+        $this->extension('flarum-testing-tests');
+
+        $enabled = $this->app()->getContainer()->make('flarum.extensions')->isEnabled('flarum-testing-tests');
+        $this->assertTrue($enabled);
+    }
+
+    /**
+     * @test
+     */
+    public function can_apply_extenders()
+    {
+        $this->extend(
+            (new Extend\Settings)->serializeToForum('notARealSetting', 'not.a.real.setting')
+        );
+
+        $response = $this->send(
+            $this->request('GET', '/')
+        );
+
+        $this->assertStringContainsString('notARealSetting', $response->getBody()->getContents());
+    }
+
+    /**
+     * @test
+     */
+    public function can_apply_route_extenders()
+    {
+        $this->extend(
+            (new Extend\Frontend('forum'))->route('/arbitrary', 'arbitrary')
+        );
+
+        $response = $this->send(
+            $this->request('GET', '/arbitrary')
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function routes_added_by_current_extension_not_accessible_by_default()
+    {
+        $response = $this->send(
+            $this->request('GET', '/added-by-extension')
+        );
+
+        $this->assertEquals(404, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function routes_added_by_current_extension_accessible()
+    {
+        $this->extension('flarum-testing-tests');
+    
+        $response = $this->send(
+            $this->request('GET', '/added-by-extension')
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function extension_url_correct()
+    {
+        $this->extension('flarum-testing-tests');
+        $expected = $this->app()->getContainer()->make('filesystem')->disk('flarum-assets')->url('/flarum-testing-tests/');
+        // We need to test this since we override it.
+        $extensions = $this->app()->getContainer()->make('flarum.extensions');
+        $currExtension = $extensions->getExtension('flarum-testing-tests');
+        $baseAssetsUrl = $extensions->getAsset($currExtension, '');
+
+        $this->assertEquals($expected, $baseAssetsUrl);
+    }
+}
\ No newline at end of file
diff --git a/php-packages/testing/tests/tests/integration/setup.php b/php-packages/testing/tests/tests/integration/setup.php
new file mode 100644
index 000000000..67039c083
--- /dev/null
+++ b/php-packages/testing/tests/tests/integration/setup.php
@@ -0,0 +1,16 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+use Flarum\Testing\integration\Setup\SetupScript;
+
+require __DIR__.'/../../vendor/autoload.php';
+
+$setup = new SetupScript();
+
+$setup->run();
diff --git a/php-packages/testing/tests/tests/phpunit.integration.xml b/php-packages/testing/tests/tests/phpunit.integration.xml
new file mode 100644
index 000000000..23afc237d
--- /dev/null
+++ b/php-packages/testing/tests/tests/phpunit.integration.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
+    backupGlobals="false"
+    backupStaticAttributes="false"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    processIsolation="true"
+    stopOnFailure="false"
+>
+    <coverage processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">../src/</directory>
+        </include>
+    </coverage>
+    <testsuites>
+        <testsuite name="Flarum Integration Tests">
+            <directory suffix="Test.php">./integration</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>
diff --git a/php-packages/testing/tests/tests/phpunit.unit.xml b/php-packages/testing/tests/tests/phpunit.unit.xml
new file mode 100644
index 000000000..d3a4a3e3d
--- /dev/null
+++ b/php-packages/testing/tests/tests/phpunit.unit.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd"
+    backupGlobals="false"
+    backupStaticAttributes="false"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    processIsolation="false"
+    stopOnFailure="false"
+>
+    <coverage processUncoveredFiles="true">
+        <include>
+            <directory suffix=".php">../src/</directory>
+        </include>
+    </coverage>
+    <testsuites>
+        <testsuite name="Flarum Unit Tests">
+            <directory suffix="Test.php">./unit</directory>
+        </testsuite>
+    </testsuites>
+    <listeners>
+        <listener class="\Mockery\Adapter\Phpunit\TestListener" />
+    </listeners>
+</phpunit>
diff --git a/php-packages/testing/tests/tests/unit/.gitkeep b/php-packages/testing/tests/tests/unit/.gitkeep
new file mode 100644
index 000000000..e69de29bb