diff --git a/composer.json b/composer.json
index 99388c72..3cab6524 100644
--- a/composer.json
+++ b/composer.json
@@ -15,9 +15,23 @@
         "php": ">=8.1"
     },
     "require-dev": {
+        "phpunit/phpunit": "^10.5",
         "squizlabs/php_codesniffer": "^3.7",
         "phpstan/phpstan": "^1.10",
-        "joomla/coding-standards": "^4.0"
+        "joomla/coding-standards": "dev-3.x-dev"
+    },
+    "autoload": {
+        "psr-4": {
+            "Joomla\\Component\\MokoSuiteCross\\Administrator\\": "source/packages/com_mokosuitecross/src/",
+            "Joomla\\Component\\MokoSuiteCross\\Site\\": "source/packages/com_mokosuitecross/site/src/",
+            "Joomla\\Plugin\\Content\\MokoSuiteCross\\": "source/packages/plg_content_mokosuitecross/src/",
+            "Joomla\\Plugin\\System\\MokoSuiteCross\\": "source/packages/plg_system_mokosuitecross/src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "MokoSuiteCross\\Tests\\": "tests/"
+        }
     },
     "config": {
         "sort-packages": true
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
new file mode 100644
index 00000000..a8b7ba93
--- /dev/null
+++ b/phpunit.xml.dist
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="tests/bootstrap.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache"
+         executionOrder="depends,defects"
+         failOnRisky="true"
+         failOnWarning="true">
+    <testsuites>
+        <testsuite name="Unit">
+            <directory>tests/Unit</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory>source/packages/com_mokosuitecross/src</directory>
+            <directory>source/packages/plg_content_mokosuitecross/src</directory>
+            <directory>source/packages/plg_system_mokosuitecross/src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/tests/Unit/Helper/PreviewHelperTest.php b/tests/Unit/Helper/PreviewHelperTest.php
new file mode 100644
index 00000000..7d3d8dfa
--- /dev/null
+++ b/tests/Unit/Helper/PreviewHelperTest.php
@@ -0,0 +1,128 @@
+<?php
+
+/**
+ * @package     MokoSuiteCross
+ * @subpackage  Tests
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+namespace MokoSuiteCross\Tests\Unit\Helper;
+
+use Joomla\Component\MokoSuiteCross\Administrator\Helper\PreviewHelper;
+use PHPUnit\Framework\Attributes\RequiresMethod;
+use PHPUnit\Framework\TestCase;
+
+#[RequiresMethod(PreviewHelper::class, 'render')]
+class PreviewHelperTest extends TestCase
+{
+    public function testRenderTwitterContainsCharCount(): void
+    {
+        $html = PreviewHelper::render('twitter', 'Test Title', 'Hello world', 'https://example.com', '', 'Author');
+
+        $this->assertStringContainsString('11/280', $html);
+    }
+
+    public function testRenderTwitterEscapesHtml(): void
+    {
+        $html = PreviewHelper::render('twitter', '<script>alert(1)</script>', 'text', 'https://example.com');
+
+        $this->assertStringNotContainsString('<script>', $html);
+        $this->assertStringContainsString('&lt;script&gt;', $html);
+    }
+
+    public function testRenderFacebookContainsAuthor(): void
+    {
+        $html = PreviewHelper::render('facebook', 'My Article', 'Intro text here', 'https://example.com', '', 'John Doe');
+
+        $this->assertStringContainsString('John Doe', $html);
+        $this->assertStringContainsString('My Article', $html);
+    }
+
+    public function testRenderMastodonContainsCharCount(): void
+    {
+        $html = PreviewHelper::render('mastodon', 'Title', 'Post text', 'https://example.com', '', 'Author');
+
+        $this->assertStringContainsString('9/500', $html);
+    }
+
+    public function testRenderBlueskyContainsCharCount(): void
+    {
+        $html = PreviewHelper::render('bluesky', 'Title', 'A bluesky post', 'https://example.com', '', 'Author');
+
+        $this->assertStringContainsString('14/300', $html);
+    }
+
+    public function testRenderLinkedInContainsAuthor(): void
+    {
+        $html = PreviewHelper::render('linkedin', 'Article', 'Text', 'https://example.com', '', 'Jane Smith');
+
+        $this->assertStringContainsString('Jane Smith', $html);
+    }
+
+    public function testRenderTelegramDoesNotShowAuthor(): void
+    {
+        $html = PreviewHelper::render('telegram', 'Article', 'Message text', 'https://example.com');
+
+        $this->assertStringContainsString('Message text', $html);
+        $this->assertStringContainsString('Article', $html);
+    }
+
+    public function testRenderWithImageIncludesImgTag(): void
+    {
+        $html = PreviewHelper::render('twitter', 'Title', 'Text', 'https://example.com', 'https://example.com/image.jpg', 'Author');
+
+        $this->assertStringContainsString('<img src="https://example.com/image.jpg"', $html);
+    }
+
+    public function testRenderWithoutImageOmitsImgTag(): void
+    {
+        $html = PreviewHelper::render('twitter', 'Title', 'Text', 'https://example.com', '', 'Author');
+
+        $this->assertStringNotContainsString('<img', $html);
+    }
+
+    public function testRenderGenericPlatform(): void
+    {
+        $html = PreviewHelper::render('pinterest', 'Title', 'Text', 'https://example.com');
+
+        $this->assertStringContainsString('PINTEREST', $html);
+        $this->assertStringContainsString('Title', $html);
+    }
+
+    public function testGetSupportedPlatformsReturnsSix(): void
+    {
+        $platforms = PreviewHelper::getSupportedPlatforms();
+
+        $this->assertCount(6, $platforms);
+        $this->assertContains('twitter', $platforms);
+        $this->assertContains('facebook', $platforms);
+        $this->assertContains('mastodon', $platforms);
+        $this->assertContains('linkedin', $platforms);
+        $this->assertContains('bluesky', $platforms);
+        $this->assertContains('telegram', $platforms);
+    }
+
+    public function testRenderUsesTextWhenProvided(): void
+    {
+        $html = PreviewHelper::render('facebook', 'My Title', 'Custom intro text', 'https://example.com');
+
+        $this->assertStringContainsString('Custom intro text', $html);
+    }
+
+    public function testRenderFallsBackToTitleWhenTextEmpty(): void
+    {
+        $html = PreviewHelper::render('facebook', 'Fallback Title', '', 'https://example.com');
+
+        $this->assertMatchesRegularExpression('/Fallback Title.*Fallback Title/s', $html);
+    }
+
+    public function testImageUrlIsEscaped(): void
+    {
+        $html = PreviewHelper::render('twitter', 'Title', 'Text', 'https://example.com', 'https://example.com/img?a=1&b=2', 'Author');
+
+        $this->assertStringContainsString('https://example.com/img?a=1&amp;b=2', $html);
+    }
+}
diff --git a/tests/Unit/Helper/ServiceIconHelperTest.php b/tests/Unit/Helper/ServiceIconHelperTest.php
new file mode 100644
index 00000000..0aa82838
--- /dev/null
+++ b/tests/Unit/Helper/ServiceIconHelperTest.php
@@ -0,0 +1,69 @@
+<?php
+
+/**
+ * @package     MokoSuiteCross
+ * @subpackage  Tests
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+namespace MokoSuiteCross\Tests\Unit\Helper;
+
+use Joomla\Component\MokoSuiteCross\Administrator\Helper\ServiceIconHelper;
+use PHPUnit\Framework\TestCase;
+
+class ServiceIconHelperTest extends TestCase
+{
+    /**
+     * @dataProvider knownServiceTypesProvider
+     */
+    public function testGetIconReturnsKnownIcon(string $serviceType, string $expectedIcon): void
+    {
+        $this->assertSame($expectedIcon, ServiceIconHelper::getIcon($serviceType));
+    }
+
+    public static function knownServiceTypesProvider(): array
+    {
+        return [
+            'facebook'  => ['facebook', 'icon-facebook'],
+            'twitter'   => ['twitter', 'icon-twitter'],
+            'linkedin'  => ['linkedin', 'icon-linkedin'],
+            'mastodon'  => ['mastodon', 'icon-globe'],
+            'bluesky'   => ['bluesky', 'icon-cloud'],
+            'telegram'  => ['telegram', 'icon-paper-plane'],
+            'discord'   => ['discord', 'icon-headset'],
+            'slack'     => ['slack', 'icon-hashtag'],
+            'mailchimp' => ['mailchimp', 'icon-envelope'],
+            'medium'    => ['medium', 'icon-book'],
+        ];
+    }
+
+    public function testGetIconReturnsFallbackForUnknownType(): void
+    {
+        $this->assertSame('icon-share-alt', ServiceIconHelper::getIcon('unknown_platform'));
+    }
+
+    public function testRenderIconOutputsSpanElement(): void
+    {
+        $html = ServiceIconHelper::renderIcon('facebook');
+
+        $this->assertSame('<span class="icon-facebook" aria-hidden="true"></span>', $html);
+    }
+
+    public function testRenderIconWithExtraClass(): void
+    {
+        $html = ServiceIconHelper::renderIcon('twitter', 'me-1 text-info');
+
+        $this->assertSame('<span class="icon-twitter me-1 text-info" aria-hidden="true"></span>', $html);
+    }
+
+    public function testRenderIconEscapesExtraClass(): void
+    {
+        $html = ServiceIconHelper::renderIcon('facebook', '"><script>');
+
+        $this->assertStringNotContainsString('<script>', $html);
+        $this->assertStringContainsString('&quot;&gt;&lt;script&gt;', $html);
+    }
+}
diff --git a/tests/Unit/Service/ServiceInterfaceContractTest.php b/tests/Unit/Service/ServiceInterfaceContractTest.php
new file mode 100644
index 00000000..28dd7809
--- /dev/null
+++ b/tests/Unit/Service/ServiceInterfaceContractTest.php
@@ -0,0 +1,128 @@
+<?php
+
+/**
+ * @package     MokoSuiteCross
+ * @subpackage  Tests
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+namespace MokoSuiteCross\Tests\Unit\Service;
+
+use Joomla\Component\MokoSuiteCross\Administrator\Service\MokoSuiteCrossServiceInterface;
+use PHPUnit\Framework\TestCase;
+
+class ServiceInterfaceContractTest extends TestCase
+{
+    public function testInterfaceExists(): void
+    {
+        $this->assertTrue(interface_exists(MokoSuiteCrossServiceInterface::class));
+    }
+
+    public function testInterfaceDefinesRequiredMethods(): void
+    {
+        $reflection = new \ReflectionClass(MokoSuiteCrossServiceInterface::class);
+
+        $expectedMethods = [
+            'getServiceType',
+            'getServiceName',
+            'publish',
+            'validateCredentials',
+            'getMaxLength',
+            'supportsMedia',
+            'getSupportedMediaTypes',
+        ];
+
+        foreach ($expectedMethods as $method) {
+            $this->assertTrue(
+                $reflection->hasMethod($method),
+                "Interface missing method: {$method}"
+            );
+        }
+    }
+
+    public function testGetServiceTypeReturnsString(): void
+    {
+        $method = new \ReflectionMethod(MokoSuiteCrossServiceInterface::class, 'getServiceType');
+        $returnType = $method->getReturnType();
+
+        $this->assertNotNull($returnType);
+        $this->assertSame('string', $returnType->getName());
+    }
+
+    public function testPublishAcceptsCorrectParameters(): void
+    {
+        $method = new \ReflectionMethod(MokoSuiteCrossServiceInterface::class, 'publish');
+        $params = $method->getParameters();
+
+        $this->assertCount(4, $params);
+        $this->assertSame('message', $params[0]->getName());
+        $this->assertSame('media', $params[1]->getName());
+        $this->assertSame('credentials', $params[2]->getName());
+        $this->assertSame('params', $params[3]->getName());
+    }
+
+    public function testPublishReturnsArray(): void
+    {
+        $method = new \ReflectionMethod(MokoSuiteCrossServiceInterface::class, 'publish');
+        $returnType = $method->getReturnType();
+
+        $this->assertNotNull($returnType);
+        $this->assertSame('array', $returnType->getName());
+    }
+
+    public function testGetMaxLengthReturnsInt(): void
+    {
+        $method = new \ReflectionMethod(MokoSuiteCrossServiceInterface::class, 'getMaxLength');
+        $returnType = $method->getReturnType();
+
+        $this->assertNotNull($returnType);
+        $this->assertSame('int', $returnType->getName());
+    }
+
+    public function testSupportsMediaReturnsBool(): void
+    {
+        $method = new \ReflectionMethod(MokoSuiteCrossServiceInterface::class, 'supportsMedia');
+        $returnType = $method->getReturnType();
+
+        $this->assertNotNull($returnType);
+        $this->assertSame('bool', $returnType->getName());
+    }
+
+    /**
+     * @dataProvider servicePluginClassProvider
+     */
+    public function testServicePluginImplementsInterface(string $className): void
+    {
+        if (!class_exists($className)) {
+            $this->markTestSkipped("Class {$className} not autoloadable (needs Joomla runtime)");
+        }
+
+        $this->assertTrue(
+            is_subclass_of($className, MokoSuiteCrossServiceInterface::class),
+            "{$className} does not implement MokoSuiteCrossServiceInterface"
+        );
+    }
+
+    public static function servicePluginClassProvider(): array
+    {
+        $plugins = [
+            'facebook', 'twitter', 'linkedin', 'mastodon', 'bluesky',
+            'telegram', 'discord', 'slack', 'mailchimp', 'medium',
+            'instagram', 'youtube', 'threads', 'pinterest', 'reddit',
+        ];
+
+        $cases = [];
+
+        foreach ($plugins as $plugin) {
+            $class = ucfirst($plugin);
+            $cases[$plugin] = [
+                "Joomla\\Plugin\\MokoSuiteCross\\{$class}\\Extension\\{$class}Service",
+            ];
+        }
+
+        return $cases;
+    }
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
new file mode 100644
index 00000000..bfcdc914
--- /dev/null
+++ b/tests/bootstrap.php
@@ -0,0 +1,16 @@
+<?php
+
+/**
+ * @package     MokoSuiteCross
+ * @subpackage  Tests
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+if (!defined('_JEXEC')) {
+    define('_JEXEC', 1);
+}