diff --git a/module/Core/test/Domain/DomainServiceTest.php b/module/Core/test/Domain/DomainServiceTest.php
new file mode 100644
index 00000000..e91c3281
--- /dev/null
+++ b/module/Core/test/Domain/DomainServiceTest.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\Core\Domain;
+
+use Doctrine\ORM\EntityManagerInterface;
+use PHPUnit\Framework\TestCase;
+use Prophecy\Prophecy\ObjectProphecy;
+use Shlinkio\Shlink\Core\Domain\DomainService;
+use Shlinkio\Shlink\Core\Domain\Repository\DomainRepositoryInterface;
+use Shlinkio\Shlink\Core\Entity\Domain;
+
+class DomainServiceTest extends TestCase
+{
+    private DomainService $domainService;
+    private ObjectProphecy $em;
+
+    public function setUp(): void
+    {
+        $this->em = $this->prophesize(EntityManagerInterface::class);
+        $this->domainService = new DomainService($this->em->reveal());
+    }
+
+    /**
+     * @test
+     * @dataProvider provideExcludedDomains
+     */
+    public function listDomainsWithoutDelegatesIntoRepository(?string $excludedDomain, array $expectedResult): void
+    {
+        $repo = $this->prophesize(DomainRepositoryInterface::class);
+        $getRepo = $this->em->getRepository(Domain::class)->willReturn($repo->reveal());
+        $findDomains = $repo->findDomainsWithout($excludedDomain)->willReturn($expectedResult);
+
+        $result = $this->domainService->listDomainsWithout($excludedDomain);
+
+        self::assertEquals($expectedResult, $result);
+        $getRepo->shouldHaveBeenCalledOnce();
+        $findDomains->shouldHaveBeenCalledOnce();
+    }
+
+    public function provideExcludedDomains(): iterable
+    {
+        yield 'no excluded domain' => [null, []];
+        yield 'foo.com excluded domain' => ['foo.com', []];
+        yield 'bar.com excluded domain' => ['bar.com', [new Domain('bar.com')]];
+        yield 'baz.com excluded domain' => ['baz.com', [new Domain('foo.com'), new Domain('bar.com')]];
+    }
+}
diff --git a/module/Rest/test/Action/Domain/ListDomainsActionTest.php b/module/Rest/test/Action/Domain/ListDomainsActionTest.php
new file mode 100644
index 00000000..fe8ffa07
--- /dev/null
+++ b/module/Rest/test/Action/Domain/ListDomainsActionTest.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\Rest\Action\Domain;
+
+use Laminas\Diactoros\Response\JsonResponse;
+use Laminas\Diactoros\ServerRequestFactory;
+use PHPUnit\Framework\TestCase;
+use Prophecy\Prophecy\ObjectProphecy;
+use Shlinkio\Shlink\Core\Domain\DomainServiceInterface;
+use Shlinkio\Shlink\Core\Entity\Domain;
+use Shlinkio\Shlink\Rest\Action\Domain\ListDomainsAction;
+
+class ListDomainsActionTest extends TestCase
+{
+    private ListDomainsAction $action;
+    private ObjectProphecy $domainService;
+
+    public function setUp(): void
+    {
+        $this->domainService = $this->prophesize(DomainServiceInterface::class);
+        $this->action = new ListDomainsAction($this->domainService->reveal(), 'foo.com');
+    }
+
+    /** @test */
+    public function domainsAreProperlyListed(): void
+    {
+        $listDomains = $this->domainService->listDomainsWithout('foo.com')->willReturn([
+            new Domain('bar.com'),
+            new Domain('baz.com'),
+        ]);
+
+        /** @var JsonResponse $resp */
+        $resp = $this->action->handle(ServerRequestFactory::fromGlobals());
+        $payload = $resp->getPayload();
+
+        self::assertEquals([
+            'domains' => [
+                'data' => [
+                    [
+                        'domain' => 'foo.com',
+                        'isDefault' => true,
+                    ],
+                    [
+                        'domain' => 'bar.com',
+                        'isDefault' => false,
+                    ],
+                    [
+                        'domain' => 'baz.com',
+                        'isDefault' => false,
+                    ],
+                ],
+            ],
+        ], $payload);
+        $listDomains->shouldHaveBeenCalledOnce();
+    }
+}