diff --git a/src/test/java/mops/gruppen2/domain/service/helper/ProjectionHelperTest.java b/src/test/java/mops/gruppen2/domain/service/helper/ProjectionHelperTest.java
new file mode 100644
index 0000000..1d2d5b4
--- /dev/null
+++ b/src/test/java/mops/gruppen2/domain/service/helper/ProjectionHelperTest.java
@@ -0,0 +1,210 @@
+package mops.gruppen2.domain.service.helper;
+
+import mops.gruppen2.domain.event.AddMemberEvent;
+import mops.gruppen2.domain.event.CreateGroupEvent;
+import mops.gruppen2.domain.event.Event;
+import mops.gruppen2.domain.event.SetLimitEvent;
+import mops.gruppen2.domain.event.UpdateRoleEvent;
+import mops.gruppen2.domain.model.group.Group;
+import mops.gruppen2.domain.model.group.Role;
+import mops.gruppen2.domain.model.group.User;
+import mops.gruppen2.domain.model.group.wrapper.Limit;
+import mops.gruppen2.infrastructure.GroupCache;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+
+import static mops.gruppen2.TestHelper.initEvents;
+import static mops.gruppen2.TestHelper.uuid;
+import static mops.gruppen2.domain.service.helper.ProjectionHelper.project;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+class ProjectionHelperTest {
+
+    @BeforeEach
+    void setUp() {
+    }
+
+    @Test
+    void project_nocache_emptyList() {
+        assertThat(project(Collections.emptyList())).isEmpty();
+    }
+
+    @Test
+    void project_nocache_oneCreate() {
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()));
+
+        initEvents(events);
+
+        assertThat(project(events)).hasSize(1);
+    }
+
+    @Test
+    void project_nocache_multipleCreate() {
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(2), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(3), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(4), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(5), "TEST", LocalDateTime.now()));
+
+        initEvents(events);
+
+        assertThat(project(events)).hasSize(5);
+    }
+
+    @Test
+    void project_nocache_oneDetailed() {
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(1), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(1), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(1), "TEST", new Limit(5)));
+
+        initEvents(events);
+
+        List<Group> groups = project(events);
+
+        assertThat(groups).hasSize(1);
+        assertThat(groups.get(0).exists()).isTrue();
+        assertThat(groups.get(0).getAdmins()).hasSize(1);
+        assertThat(groups.get(0).getLimit()).isEqualTo(5);
+    }
+
+    @Test
+    void project_nocache_multipleDetailed() {
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(1), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(1), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(1), "TEST", new Limit(5)),
+
+                new CreateGroupEvent(uuid(2), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(2), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(2), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(2), "TEST", new Limit(15)),
+
+                new CreateGroupEvent(uuid(3), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(3), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(3), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(3), "TEST", new Limit(25)),
+
+                new CreateGroupEvent(uuid(4), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(4), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(4), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(4), "TEST", new Limit(35)));
+
+        initEvents(events);
+
+        List<Group> groups = project(events);
+
+        assertThat(groups).hasSize(4);
+        assertThat(groups.get(0).exists()).isTrue();
+        assertThat(groups.get(0).getAdmins()).hasSize(1);
+        assertThat(groups.get(0).getLimit()).isEqualTo(5);
+
+        assertThat(groups.get(1).exists()).isTrue();
+        assertThat(groups.get(1).getAdmins()).hasSize(1);
+        assertThat(groups.get(1).getLimit()).isEqualTo(15);
+
+        assertThat(groups.get(2).exists()).isTrue();
+        assertThat(groups.get(2).getAdmins()).hasSize(1);
+        assertThat(groups.get(2).getLimit()).isEqualTo(25);
+
+        assertThat(groups.get(3).exists()).isTrue();
+        assertThat(groups.get(3).getAdmins()).hasSize(1);
+        assertThat(groups.get(3).getLimit()).isEqualTo(35);
+    }
+
+    @Test
+    void project_cache_noGroups() {
+        Map<UUID, Group> groups = new HashMap<>();
+
+        project(groups, Collections.emptyList(), mock(GroupCache.class));
+
+        assertThat(groups).isEmpty();
+    }
+
+    @Test
+    void project_cache_oneCreate() {
+        Map<UUID, Group> groups = new HashMap<>();
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()));
+
+        initEvents(events);
+        project(groups, events, mock(GroupCache.class));
+
+        assertThat(groups).hasSize(1);
+        assertThat(groups.keySet()).containsExactly(uuid(1));
+    }
+
+    @Test
+    void project_cache_multipleCreate() {
+        Map<UUID, Group> groups = new HashMap<>();
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(2), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(3), "TEST", LocalDateTime.now()),
+                new CreateGroupEvent(uuid(4), "TEST", LocalDateTime.now()));
+
+        initEvents(events);
+        project(groups, events, mock(GroupCache.class));
+
+        assertThat(groups).hasSize(4);
+        assertThat(groups.keySet()).containsExactly(uuid(1), uuid(2), uuid(3), uuid(4));
+    }
+
+    @Test
+    void project_cache_multipleDetailed() {
+        Map<UUID, Group> groups = new HashMap<>();
+        List<Event> events = Arrays.asList(
+                new CreateGroupEvent(uuid(1), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(1), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(1), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(1), "TEST", new Limit(5)),
+
+                new CreateGroupEvent(uuid(2), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(2), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(2), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(2), "TEST", new Limit(15)),
+
+                new CreateGroupEvent(uuid(3), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(3), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(3), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(3), "TEST", new Limit(25)),
+
+                new CreateGroupEvent(uuid(4), "TEST", LocalDateTime.now()),
+                new AddMemberEvent(uuid(4), "TEST", "TEST", new User("TEST")),
+                new UpdateRoleEvent(uuid(4), "TEST", "TEST", Role.ADMIN),
+                new SetLimitEvent(uuid(4), "TEST", new Limit(35)));
+
+        initEvents(events);
+        project(groups, events, mock(GroupCache.class));
+
+        assertThat(groups).hasSize(4);
+        assertThat(groups.get(uuid(1)).exists()).isTrue();
+        assertThat(groups.get(uuid(1)).getAdmins()).hasSize(1);
+        assertThat(groups.get(uuid(1)).getLimit()).isEqualTo(5);
+
+        assertThat(groups.get(uuid(2)).exists()).isTrue();
+        assertThat(groups.get(uuid(2)).getAdmins()).hasSize(1);
+        assertThat(groups.get(uuid(2)).getLimit()).isEqualTo(15);
+
+        assertThat(groups.get(uuid(3)).exists()).isTrue();
+        assertThat(groups.get(uuid(3)).getAdmins()).hasSize(1);
+        assertThat(groups.get(uuid(3)).getLimit()).isEqualTo(25);
+
+        assertThat(groups.get(uuid(4)).exists()).isTrue();
+        assertThat(groups.get(uuid(4)).getAdmins()).hasSize(1);
+        assertThat(groups.get(uuid(4)).getLimit()).isEqualTo(35);
+    }
+}