diff --git a/backend/tests/Unit/User/UseCases/SearchUsersTest.php b/backend/tests/Unit/User/UseCases/SearchUsersTest.php
new file mode 100644
index 0000000..6d0cbed
--- /dev/null
+++ b/backend/tests/Unit/User/UseCases/SearchUsersTest.php
@@ -0,0 +1,95 @@
+<?php
+
+namespace Tests\Unit\User\UseCases;
+
+use App\Exceptions\BadRequestException;
+use App\Shared\ValueObject\EmailAddress;
+use App\User\CreateUserDto;
+use App\User\UseCases\SearchUsers\SearchUsers;
+use App\User\UseCases\SearchUsers\SearchUsersRequest;
+use Tests\Fakes\FakeUserRepository;
+use Tests\TestCase;
+
+class SearchUsersTest extends TestCase
+{
+    private FakeUserRepository $userRepo;
+
+    private SearchUsers $useCase;
+
+    protected function setUp(): void
+    {
+        $this->userRepo = new FakeUserRepository;
+        $this->useCase = new SearchUsers($this->userRepo);
+
+        $this->userRepo->create(new CreateUserDto(
+            email: new EmailAddress('alice@example.com'),
+            displayName: 'alice',
+            passwordHash: '',
+            isAdmin: false,
+            emailConfirmedAt: null,
+        ));
+        $this->userRepo->create(new CreateUserDto(
+            email: new EmailAddress('alex@example.com'),
+            displayName: 'alex',
+            passwordHash: '',
+            isAdmin: false,
+            emailConfirmedAt: null,
+        ));
+        $this->userRepo->create(new CreateUserDto(
+            email: new EmailAddress('bob@other.com'),
+            displayName: 'bob',
+            passwordHash: '',
+            isAdmin: false,
+            emailConfirmedAt: null,
+        ));
+    }
+
+    public function test_blank_query_throws_bad_request(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->useCase->execute(new SearchUsersRequest(query: '   '));
+    }
+
+    public function test_finds_users_by_display_name_prefix(): void
+    {
+        $results = $this->useCase->execute(new SearchUsersRequest(
+            query: 'al',
+        ));
+
+        $this->assertCount(2, $results);
+        $names = array_map(
+            function ($user) {
+                return $user->getDisplayName();
+            },
+            $results,
+        );
+        sort($names);
+        $this->assertSame(['alex', 'alice'], $names);
+    }
+
+    public function test_search_is_case_insensitive(): void
+    {
+        $results = $this->useCase->execute(new SearchUsersRequest(
+            query: 'ALI',
+        ));
+        $this->assertCount(1, $results);
+        $this->assertSame('alice', $results[0]->getDisplayName());
+    }
+
+    public function test_finds_users_by_email_prefix(): void
+    {
+        $results = $this->useCase->execute(new SearchUsersRequest(
+            query: 'bob@',
+        ));
+        $this->assertCount(1, $results);
+        $this->assertSame('bob', $results[0]->getDisplayName());
+    }
+
+    public function test_no_results_when_no_match(): void
+    {
+        $results = $this->useCase->execute(new SearchUsersRequest(
+            query: 'zzz',
+        ));
+        $this->assertSame([], $results);
+    }
+}