diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..3dbb040
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,61 @@
+"""Shared pytest fixtures."""
+
+import pytest
+
+from src.models.conversation import ConversationState, ChatMessage
+from src.models.registration import (
+    RegistrationData,
+    ChildInfo,
+    ParentGuardian,
+    EmergencyContact,
+    Booking,
+    BookingDay,
+)
+
+
+@pytest.fixture
+def complete_registration() -> RegistrationData:
+    """A fully populated RegistrationData that passes is_complete()."""
+    return RegistrationData(
+        child=ChildInfo(
+            full_name="Lena Muster",
+            date_of_birth="2022-03-15",
+            special_needs="None",
+        ),
+        parent_guardian=ParentGuardian(
+            full_name="Anna Muster",
+            street_address="Hauptstrasse 1",
+            postal_code="8117",
+            city="Fällanden",
+            phone="044 123 45 67",
+            email="anna.muster@example.com",
+        ),
+        emergency_contact=EmergencyContact(
+            full_name="Hans Muster",
+            phone="079 123 45 67",
+        ),
+        booking=Booking(
+            playgroup_types=["indoor"],
+            selected_days=[BookingDay(day="monday", type="indoor")],
+        ),
+    )
+
+
+@pytest.fixture
+def fresh_state() -> ConversationState:
+    """A brand-new ConversationState for a parent email."""
+    return ConversationState(
+        conversation_id="anna.muster@example.com",
+        parent_email="anna.muster@example.com",
+    )
+
+
+@pytest.fixture
+def state_with_messages(fresh_state) -> ConversationState:
+    """A ConversationState with a couple of chat turns."""
+    fresh_state.messages = [
+        ChatMessage(role="user", content="Hallo, ich möchte mein Kind anmelden."),
+        ChatMessage(role="assistant", content="Hallo! Wie heisst dein Kind?"),
+        ChatMessage(role="user", content="Lena Muster"),
+    ]
+    return fresh_state
diff --git a/tests/test_agent.py b/tests/test_agent.py
new file mode 100644
index 0000000..64604ef
--- /dev/null
+++ b/tests/test_agent.py
@@ -0,0 +1,271 @@
+"""Tests for EmailAgent — the conversation orchestrator."""
+
+import json
+import pytest
+
+from unittest.mock import MagicMock, patch
+
+from src.agent.core import EmailAgent
+from src.models.conversation import ConversationState
+
+
+# ---------------------------------------------------------------------------
+# Helpers / fixtures
+# ---------------------------------------------------------------------------
+
+VALID_LLM_REPLY = json.dumps({
+    "reply": "Wie heisst dein Kind?",
+    "updates": {},
+    "next_step": "child_name",
+    "registration_complete": False,
+    "language": "de",
+})
+
+COMPLETION_LLM_REPLY = json.dumps({
+    "reply": "Vielen Dank, dein Kind ist angemeldet!",
+    "updates": {},
+    "next_step": "done",
+    "registration_complete": True,
+    "language": "de",
+})
+
+
+@pytest.fixture
+def mock_kb():
+    kb = MagicMock()
+    kb.get_all.return_value = "# FAQ\nSome knowledge base content."
+    return kb
+
+
+@pytest.fixture
+def mock_store():
+    store = MagicMock()
+    store.load.return_value = None  # no prior conversation by default
+    store.save_registration.return_value = ("anna.muster@example.com", 1)
+    return store
+
+
+@pytest.fixture
+def mock_notifier():
+    return MagicMock()
+
+
+@pytest.fixture
+def agent(mock_kb, mock_store, mock_notifier):
+    return EmailAgent(
+        model="anthropic/claude-opus-4-6",
+        kb=mock_kb,
+        store=mock_store,
+        notifier=mock_notifier,
+    )
+
+
+# ---------------------------------------------------------------------------
+# process_message — new conversation
+# ---------------------------------------------------------------------------
+
+
+class TestProcessMessageNewConversation:
+    def test_creates_new_state_when_none_exists(self, agent, mock_store):
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Hallo")
+
+        saved_state = mock_store.save.call_args[0][0]
+        assert saved_state.conversation_id == "anna.muster@example.com"
+
+    def test_returns_llm_reply_text(self, agent):
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            reply = agent.process_message("anna.muster@example.com", "Hallo")
+
+        assert reply == "Wie heisst dein Kind?"
+
+    def test_user_message_added_to_history(self, agent, mock_store):
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Hallo, ich möchte anmelden")
+
+        state = mock_store.save.call_args[0][0]
+        assert any(m.role == "user" and "anmelden" in m.content for m in state.messages)
+
+    def test_assistant_reply_added_to_history(self, agent, mock_store):
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Hallo")
+
+        state = mock_store.save.call_args[0][0]
+        assert any(m.role == "assistant" for m in state.messages)
+
+    def test_normalizes_email_key(self, agent, mock_store):
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            agent.process_message("Anna.Muster@EXAMPLE.COM", "Hallo")
+
+        state = mock_store.save.call_args[0][0]
+        assert state.conversation_id == "anna.muster@example.com"
+
+
+# ---------------------------------------------------------------------------
+# process_message — existing conversation
+# ---------------------------------------------------------------------------
+
+
+class TestProcessMessageExistingConversation:
+    def test_loads_existing_state(self, agent, mock_store, fresh_state):
+        mock_store.load.return_value = fresh_state
+
+        with patch("src.llm.complete", return_value=VALID_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Lena")
+
+        mock_store.load.assert_called_once()
+
+    def test_flow_step_updated(self, agent, mock_store, fresh_state):
+        mock_store.load.return_value = fresh_state
+
+        reply_with_step = json.dumps({
+            "reply": "Wann ist Lena geboren?",
+            "updates": {"child.fullName": "Lena"},
+            "next_step": "child_dob",
+            "registration_complete": False,
+            "language": "de",
+        })
+
+        with patch("src.llm.complete", return_value=reply_with_step):
+            agent.process_message("anna.muster@example.com", "Lena")
+
+        state = mock_store.save.call_args[0][0]
+        assert state.flow_step == "child_dob"
+
+
+# ---------------------------------------------------------------------------
+# process_message — registration completion
+# ---------------------------------------------------------------------------
+
+
+class TestRegistrationCompletion:
+    def test_notifier_called_on_completion(self, agent, mock_store, mock_notifier, complete_registration):
+        state = ConversationState(
+            conversation_id="anna.muster@example.com",
+            parent_email="anna.muster@example.com",
+        )
+        state.registration = complete_registration
+        mock_store.load.return_value = state
+
+        with patch("src.llm.complete", return_value=COMPLETION_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Ja, alles korrekt")
+
+        mock_notifier.notify_admin.assert_called_once()
+
+    def test_state_marked_completed(self, agent, mock_store, complete_registration):
+        state = ConversationState(
+            conversation_id="anna.muster@example.com",
+            parent_email="anna.muster@example.com",
+        )
+        state.registration = complete_registration
+        mock_store.load.return_value = state
+
+        with patch("src.llm.complete", return_value=COMPLETION_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Ja")
+
+        saved = mock_store.save.call_args[0][0]
+        assert saved.completed is True
+
+    def test_notifier_not_called_when_already_completed(self, agent, mock_store, mock_notifier, complete_registration):
+        state = ConversationState(
+            conversation_id="anna.muster@example.com",
+            parent_email="anna.muster@example.com",
+        )
+        state.registration = complete_registration
+        state.completed = True  # already done
+        mock_store.load.return_value = state
+
+        with patch("src.llm.complete", return_value=COMPLETION_LLM_REPLY):
+            agent.process_message("anna.muster@example.com", "Noch eine Frage")
+
+        mock_notifier.notify_admin.assert_not_called()
+
+
+# ---------------------------------------------------------------------------
+# Fallback on LLM error
+# ---------------------------------------------------------------------------
+
+
+class TestFallbackOnLLMError:
+    def test_returns_german_fallback_by_default(self, agent):
+        with patch("src.llm.complete", side_effect=RuntimeError("API down")):
+            reply = agent.process_message("anna.muster@example.com", "Hallo")
+
+        assert "technisches Problem" in reply or "Entschuldigung" in reply
+
+    def test_returns_english_fallback_when_language_is_en(self, agent, mock_store, fresh_state):
+        fresh_state.language = "en"
+        mock_store.load.return_value = fresh_state
+
+        with patch("src.llm.complete", side_effect=RuntimeError("API down")):
+            reply = agent.process_message("anna.muster@example.com", "Hello")
+
+        assert "technical issue" in reply.lower() or "sorry" in reply.lower()
+
+
+# ---------------------------------------------------------------------------
+# _parse_llm_response
+# ---------------------------------------------------------------------------
+
+
+class TestParseLlmResponse:
+    def test_parses_plain_json(self, agent):
+        payload = '{"reply": "Hi", "updates": {}, "next_step": "greeting", "registration_complete": false, "language": "de"}'
+        result = agent._parse_llm_response(payload)
+        assert result["reply"] == "Hi"
+
+    def test_parses_fenced_json(self, agent):
+        payload = '```json\n{"reply": "Hi", "updates": {}}\n```'
+        result = agent._parse_llm_response(payload)
+        assert result["reply"] == "Hi"
+
+    def test_parses_json_embedded_in_text(self, agent):
+        payload = 'Sure, here is the response: {"reply": "Hi", "updates": {}}'
+        result = agent._parse_llm_response(payload)
+        assert result["reply"] == "Hi"
+
+    def test_falls_back_to_raw_text_when_no_json(self, agent):
+        result = agent._parse_llm_response("Ich bin ein Hilfsroboter")
+        assert result["reply"] == "Ich bin ein Hilfsroboter"
+
+    def test_fallback_has_safe_defaults(self, agent):
+        result = agent._parse_llm_response("plain text")
+        assert result["registration_complete"] is False
+        assert result["updates"] == {}
+
+
+# ---------------------------------------------------------------------------
+# _apply_updates
+# ---------------------------------------------------------------------------
+
+
+class TestApplyUpdates:
+    def test_sets_child_name(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {"child.fullName": "Lena Muster"})
+        assert fresh_state.registration.child.full_name == "Lena Muster"
+
+    def test_sets_child_dob(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {"child.dateOfBirth": "2022-03-15"})
+        assert fresh_state.registration.child.date_of_birth == "2022-03-15"
+
+    def test_sets_parent_email(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {"parentGuardian.email": "test@example.com"})
+        assert fresh_state.registration.parent_guardian.email == "test@example.com"
+
+    def test_sets_emergency_contact(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {"emergencyContact.phone": "079 111 22 33"})
+        assert fresh_state.registration.emergency_contact.phone == "079 111 22 33"
+
+    def test_sets_booking_days(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {
+            "booking.selectedDays": [{"day": "wednesday", "type": "indoor"}]
+        })
+        assert fresh_state.registration.booking.selected_days[0].day == "wednesday"
+
+    def test_ignores_none_values(self, agent, fresh_state):
+        fresh_state.registration.child.full_name = "Lena"
+        agent._apply_updates(fresh_state, {"child.fullName": None})
+        assert fresh_state.registration.child.full_name == "Lena"
+
+    def test_ignores_unknown_keys(self, agent, fresh_state):
+        agent._apply_updates(fresh_state, {"unknown.key": "value"})  # should not raise
diff --git a/tests/test_knowledge_base.py b/tests/test_knowledge_base.py
new file mode 100644
index 0000000..66a9693
--- /dev/null
+++ b/tests/test_knowledge_base.py
@@ -0,0 +1,52 @@
+"""Tests for KnowledgeBase loader."""
+
+import pytest
+from pathlib import Path
+
+from src.knowledge_base.loader import KnowledgeBase
+
+
+@pytest.fixture
+def kb_dir(tmp_path) -> Path:
+    """A temporary knowledge-base directory with a couple of markdown files."""
+    (tmp_path / "faq.md").write_text("# FAQ\nWann beginnt die Spielgruppe?\nIm August.")
+    (tmp_path / "fees.md").write_text("# Fees\nCHF 130 per month.")
+    return tmp_path
+
+
+@pytest.fixture
+def kb(kb_dir) -> KnowledgeBase:
+    return KnowledgeBase(kb_dir)
+
+
+class TestKnowledgeBaseLoading:
+    def test_get_all_includes_file_content(self, kb):
+        content = kb.get_all()
+        assert "FAQ" in content
+        assert "Fees" in content
+
+    def test_get_all_concatenates_multiple_files(self, kb):
+        content = kb.get_all()
+        assert "CHF 130" in content
+        assert "Spielgruppe" in content
+
+    def test_reload_picks_up_new_file(self, kb, kb_dir):
+        (kb_dir / "schedule.md").write_text("# Schedule\nMonday 9:00")
+        kb.reload()
+        assert "Schedule" in kb.get_all()
+
+    def test_empty_directory_returns_empty_string(self, tmp_path):
+        kb = KnowledgeBase(tmp_path)
+        assert kb.get_all() == "" or isinstance(kb.get_all(), str)
+
+    def test_nonexistent_directory_does_not_raise_on_init(self, tmp_path):
+        # Should either handle gracefully or raise — just must not crash silently
+        missing = tmp_path / "does_not_exist"
+        try:
+            kb = KnowledgeBase(missing)
+            kb.get_all()
+        except (FileNotFoundError, OSError):
+            pass  # Acceptable to raise on missing dir
+
+    def test_get_all_returns_string(self, kb):
+        assert isinstance(kb.get_all(), str)
diff --git a/tests/test_llm.py b/tests/test_llm.py
new file mode 100644
index 0000000..b519e9a
--- /dev/null
+++ b/tests/test_llm.py
@@ -0,0 +1,67 @@
+"""Tests for the litellm wrapper in src/llm.py."""
+
+import pytest
+
+from src import llm
+from src.models.conversation import ChatMessage
+
+
+class TestLlmComplete:
+    def test_returns_model_reply(self, mocker):
+        mock_response = mocker.MagicMock()
+        mock_response.choices[0].message.content = "Hallo! Wie heisst dein Kind?"
+        mocker.patch("litellm.completion", return_value=mock_response)
+
+        result = llm.complete("anthropic/claude-opus-4-6", "system prompt", [])
+
+        assert result == "Hallo! Wie heisst dein Kind?"
+
+    def test_passes_model_to_litellm(self, mocker):
+        mock_response = mocker.MagicMock()
+        mock_response.choices[0].message.content = "ok"
+        mock_completion = mocker.patch("litellm.completion", return_value=mock_response)
+
+        llm.complete("openai/gpt-4o", "system", [])
+
+        call_kwargs = mock_completion.call_args.kwargs
+        assert call_kwargs["model"] == "openai/gpt-4o"
+
+    def test_system_prompt_prepended_as_system_message(self, mocker):
+        mock_response = mocker.MagicMock()
+        mock_response.choices[0].message.content = "ok"
+        mock_completion = mocker.patch("litellm.completion", return_value=mock_response)
+
+        llm.complete("anthropic/claude-opus-4-6", "You are helpful.", [])
+
+        messages = mock_completion.call_args.kwargs["messages"]
+        assert messages[0] == {"role": "system", "content": "You are helpful."}
+
+    def test_chat_messages_appended_after_system(self, mocker):
+        mock_response = mocker.MagicMock()
+        mock_response.choices[0].message.content = "ok"
+        mock_completion = mocker.patch("litellm.completion", return_value=mock_response)
+
+        chat = [
+            ChatMessage(role="user", content="Hallo"),
+            ChatMessage(role="assistant", content="Guten Tag"),
+        ]
+        llm.complete("anthropic/claude-opus-4-6", "system", chat)
+
+        messages = mock_completion.call_args.kwargs["messages"]
+        assert messages[1] == {"role": "user", "content": "Hallo"}
+        assert messages[2] == {"role": "assistant", "content": "Guten Tag"}
+
+    def test_max_tokens_passed(self, mocker):
+        mock_response = mocker.MagicMock()
+        mock_response.choices[0].message.content = "ok"
+        mock_completion = mocker.patch("litellm.completion", return_value=mock_response)
+
+        llm.complete("anthropic/claude-opus-4-6", "system", [])
+
+        assert mock_completion.call_args.kwargs["max_tokens"] == 2048
+
+    def test_litellm_exception_propagates(self, mocker):
+        mocker.patch("litellm.completion", side_effect=RuntimeError("API error"))
+
+        with pytest.raises(RuntimeError, match="API error"):
+            llm.complete("anthropic/claude-opus-4-6", "system", [])
diff --git a/tests/test_models.py b/tests/test_models.py
new file mode 100644
index 0000000..fe9157f
--- /dev/null
+++ b/tests/test_models.py
@@ -0,0 +1,152 @@
+"""Tests for data models: RegistrationData and ConversationState."""
+
+import pytest
+
+from src.models.registration import (
+    RegistrationData,
+    ChildInfo,
+    ParentGuardian,
+    EmergencyContact,
+    Booking,
+    BookingDay,
+)
+from src.models.conversation import ConversationState, ChatMessage
+
+
+# ---------------------------------------------------------------------------
+# RegistrationData.is_complete()
+# ---------------------------------------------------------------------------
+
+
+class TestRegistrationDataIsComplete:
+    def test_complete_registration_passes(self, complete_registration):
+        assert complete_registration.is_complete() is True
+
+    def test_empty_registration_fails(self):
+        assert RegistrationData().is_complete() is False
+
+    def test_missing_child_name_fails(self, complete_registration):
+        complete_registration.child.full_name = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_dob_fails(self, complete_registration):
+        complete_registration.child.date_of_birth = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_special_needs_fails(self, complete_registration):
+        complete_registration.child.special_needs = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_parent_name_fails(self, complete_registration):
+        complete_registration.parent_guardian.full_name = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_parent_email_fails(self, complete_registration):
+        complete_registration.parent_guardian.email = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_emergency_contact_fails(self, complete_registration):
+        complete_registration.emergency_contact.full_name = None
+        assert complete_registration.is_complete() is False
+
+    def test_missing_booking_days_fails(self, complete_registration):
+        complete_registration.booking.selected_days = []
+        assert complete_registration.is_complete() is False
+
+    def test_missing_playgroup_types_fails(self, complete_registration):
+        complete_registration.booking.playgroup_types = []
+        assert complete_registration.is_complete() is False
+
+
+# ---------------------------------------------------------------------------
+# RegistrationData serialisation round-trip
+# ---------------------------------------------------------------------------
+
+
+class TestRegistrationDataSerialization:
+    def test_to_dict_contains_expected_keys(self, complete_registration):
+        d = complete_registration.to_dict()
+        assert "child" in d
+        assert "parentGuardian" in d
+        assert "emergencyContact" in d
+        assert "booking" in d
+
+    def test_to_dict_child_fields(self, complete_registration):
+        d = complete_registration.to_dict()
+        assert d["child"]["fullName"] == "Lena Muster"
+        assert d["child"]["dateOfBirth"] == "2022-03-15"
+        assert d["child"]["specialNeeds"] == "None"
+
+    def test_to_dict_parent_fields(self, complete_registration):
+        d = complete_registration.to_dict()
+        assert d["parentGuardian"]["email"] == "anna.muster@example.com"
+        assert d["parentGuardian"]["postalCode"] == "8117"
+
+    def test_to_dict_booking_fields(self, complete_registration):
+        d = complete_registration.to_dict()
+        assert d["booking"]["playgroupTypes"] == ["indoor"]
+        assert d["booking"]["selectedDays"] == [{"day": "monday", "type": "indoor"}]
+
+    def test_from_dict_round_trip(self, complete_registration):
+        d = complete_registration.to_dict()
+        restored = RegistrationData.from_dict(d)
+        assert restored.child.full_name == complete_registration.child.full_name
+        assert restored.parent_guardian.email == complete_registration.parent_guardian.email
+        assert restored.emergency_contact.phone == complete_registration.emergency_contact.phone
+        assert len(restored.booking.selected_days) == len(complete_registration.booking.selected_days)
+
+    def test_from_dict_outdoor_booking(self):
+        data = {
+            "child": {"fullName": "Tim", "dateOfBirth": "2021-01-01", "specialNeeds": "None"},
+            "parentGuardian": {
+                "fullName": "Eva", "streetAddress": "Seeweg 2", "postalCode": "8117",
+                "city": "Fällanden", "phone": "044 000 00 00", "email": "eva@example.com",
+            },
+            "emergencyContact": {"fullName": "Bob", "phone": "079 000 00 00"},
+            "booking": {
+                "playgroupTypes": ["outdoor"],
+                "selectedDays": [{"day": "monday", "type": "outdoor"}],
+            },
+        }
+        reg = RegistrationData.from_dict(data)
+        assert reg.booking.playgroup_types == ["outdoor"]
+        assert reg.booking.selected_days[0].day == "monday"
+
+
+# ---------------------------------------------------------------------------
+# ConversationState serialisation round-trip
+# ---------------------------------------------------------------------------
+
+
+class TestConversationStateSerialization:
+    def test_to_dict_contains_expected_keys(self, fresh_state):
+        d = fresh_state.to_dict()
+        assert "conversation_id" in d
+        assert "language" in d
+        assert "flow_step" in d
+        assert "messages" in d
+        assert "completed" in d
+
+    def test_default_language_is_german(self, fresh_state):
+        assert fresh_state.language == "de"
+
+    def test_default_flow_step_is_greeting(self, fresh_state):
+        assert fresh_state.flow_step == "greeting"
+
+    def test_default_completed_is_false(self, fresh_state):
+        assert fresh_state.completed is False
+
+    def test_from_dict_round_trip(self, state_with_messages):
+        state_with_messages.language = "en"
+        state_with_messages.flow_step = "parent_name"
+        d = state_with_messages.to_dict()
+        restored = ConversationState.from_dict(d)
+        assert restored.conversation_id == state_with_messages.conversation_id
+        assert restored.language == "en"
+        assert restored.flow_step == "parent_name"
+        assert len(restored.messages) == len(state_with_messages.messages)
+
+    def test_messages_serialized_with_role_and_content(self, state_with_messages):
+        d = state_with_messages.to_dict()
+        assert d["messages"][0]["role"] == "user"
+        assert "Hallo" in d["messages"][0]["content"]
diff --git a/tests/test_notifier.py b/tests/test_notifier.py
new file mode 100644
index 0000000..15750f6
--- /dev/null
+++ b/tests/test_notifier.py
@@ -0,0 +1,155 @@
+"""Tests for AdminNotifier helper methods."""
+
+import pytest
+
+from src.notifications.notifier import AdminNotifier
+from src.models.registration import RegistrationData, Booking, BookingDay
+
+
+@pytest.fixture
+def notifier():
+    return AdminNotifier(
+        smtp_host="smtp.example.com",
+        smtp_port=587,
+        username="agent@example.com",
+        password="secret",
+        use_tls=True,
+        from_email="agent@example.com",
+    )
+
+
+# ---------------------------------------------------------------------------
+# _recipients_for
+# ---------------------------------------------------------------------------
+
+
+class TestRecipientsFor:
+    def test_indoor_only_recipients(self, notifier):
+        recipients = notifier._recipients_for(["indoor"])
+        assert any("andrea" in r.lower() or "sigrist" in r.lower() for r in recipients)
+
+    def test_outdoor_only_recipients(self, notifier):
+        recipients = notifier._recipients_for(["outdoor"])
+        assert any("baba.laeubli" in r.lower() for r in recipients)
+
+    def test_both_includes_both_leaders(self, notifier):
+        recipients = notifier._recipients_for(["indoor", "outdoor"])
+        joined = " ".join(recipients).lower()
+        assert "andrea.sigrist" in joined
+        assert "baba.laeubli" in joined
+
+
+# ---------------------------------------------------------------------------
+# _format_types
+# ---------------------------------------------------------------------------
+
+
+class TestFormatTypes:
+    def test_indoor_label(self, notifier):
+        assert "Innen" in notifier._format_types(["indoor"]) or "indoor" in notifier._format_types(["indoor"]).lower()
+
+    def test_outdoor_label(self, notifier):
+        assert "Wald" in notifier._format_types(["outdoor"]) or "outdoor" in notifier._format_types(["outdoor"]).lower()
+
+    def test_both_labels(self, notifier):
+        result = notifier._format_types(["indoor", "outdoor"])
+        assert len(result) > 0
+
+
+# ---------------------------------------------------------------------------
+# _calculate_age
+# ---------------------------------------------------------------------------
+
+
+class TestCalculateAge:
+    def test_returns_age_string(self, notifier):
+        result = notifier._calculate_age("2022-01-01")
+        assert isinstance(result, str)
+        assert len(result) > 0
+
+    def test_invalid_dob_returns_original_string(self, notifier):
+        result = notifier._calculate_age("not-a-date")
+        assert result == "not-a-date"
+
+
+# ---------------------------------------------------------------------------
+# _calculate_monthly_fee
+# ---------------------------------------------------------------------------
+
+
+class TestCalculateMonthlyFee:
+    def test_indoor_one_day(self, notifier, complete_registration):
+        complete_registration.booking = Booking(
+            playgroup_types=["indoor"],
+            selected_days=[BookingDay(day="monday", type="indoor")],
+        )
+        fee = notifier._calculate_monthly_fee(complete_registration)
+        assert "130" in fee
+
+    def test_indoor_two_days(self, notifier, complete_registration):
+        complete_registration.booking = Booking(
+            playgroup_types=["indoor"],
+            selected_days=[
+                BookingDay(day="monday", type="indoor"),
+                BookingDay(day="wednesday", type="indoor"),
+            ],
+        )
+        fee = notifier._calculate_monthly_fee(complete_registration)
+        assert "260" in fee
+
+    def test_indoor_three_days(self, notifier, complete_registration):
+        complete_registration.booking = Booking(
+            playgroup_types=["indoor"],
+            selected_days=[
+                BookingDay(day="monday", type="indoor"),
+                BookingDay(day="wednesday", type="indoor"),
+                BookingDay(day="thursday", type="indoor"),
+            ],
+        )
+        fee = notifier._calculate_monthly_fee(complete_registration)
+        assert "390" in fee
+
+    def test_outdoor_one_day(self, notifier, complete_registration):
+        complete_registration.booking = Booking(
+            playgroup_types=["outdoor"],
+            selected_days=[BookingDay(day="monday", type="outdoor")],
+        )
+        fee = notifier._calculate_monthly_fee(complete_registration)
+        assert "250" in fee
+
+
+# ---------------------------------------------------------------------------
+# _send — SMTP interaction
+# ---------------------------------------------------------------------------
+
+
+class TestSend:
+    def test_send_calls_smtp(self, notifier, mocker):
+        # _send uses smtplib.SMTP directly (not as context manager)
+        mock_smtp_cls = mocker.patch("smtplib.SMTP")
+        mock_server = mock_smtp_cls.return_value
+
+        notifier._send(
+            to=["admin@example.com"],
+            cc=["cc@example.com"],
+            subject="Test",
+            body="Hello",
+        )
+
+        mock_server.sendmail.assert_called_once()
+
+    def test_send_includes_all_recipients(self, notifier, mocker):
+        mock_smtp_cls = mocker.patch("smtplib.SMTP")
+        mock_server = mock_smtp_cls.return_value
+
+        notifier._send(
+            to=["a@example.com"],
+            cc=["b@example.com"],
+            subject="Test",
+            body="Hello",
+        )
+
+        call_args = mock_server.sendmail.call_args
+        recipients = call_args[0][1]  # positional arg: to_addrs
+        assert "a@example.com" in recipients
+        assert "b@example.com" in recipients
diff --git a/tests/test_storage.py b/tests/test_storage.py
new file mode 100644
index 0000000..a957826
--- /dev/null
+++ b/tests/test_storage.py
@@ -0,0 +1,159 @@
+"""Tests for ConversationStore and storage helpers."""
+
+import json
+from pathlib import Path
+
+import pytest
+
+from src.storage.json_store import (
+    ConversationStore,
+    normalize_email,
+    _diff_registrations,
+)
+from src.models.conversation import ConversationState
+
+
+# ---------------------------------------------------------------------------
+# normalize_email
+# ---------------------------------------------------------------------------
+
+
+class TestNormalizeEmail:
+    def test_lowercases(self):
+        assert normalize_email("Anna.Muster@Example.COM") == "anna.muster@example.com"
+
+    def test_strips_whitespace(self):
+        assert normalize_email("  user@example.com  ") == "user@example.com"
+
+    def test_already_normalized(self):
+        assert normalize_email("user@example.com") == "user@example.com"
+
+
+# ---------------------------------------------------------------------------
+# _diff_registrations
+# ---------------------------------------------------------------------------
+
+
+class TestDiffRegistrations:
+    def test_detects_changed_field(self):
+        old = {"child": {"fullName": "Lena"}}
+        new = {"child": {"fullName": "Lena Muster"}}
+        diff = _diff_registrations(old, new)
+        assert "child.fullName" in diff
+        assert diff["child.fullName"] == ("Lena", "Lena Muster")
+
+    def test_unchanged_fields_not_included(self):
+        old = {"child": {"fullName": "Lena", "dateOfBirth": "2022-01-01"}}
+        new = {"child": {"fullName": "Lena", "dateOfBirth": "2022-01-01"}}
+        assert _diff_registrations(old, new) == {}
+
+    def test_nested_change_detected(self):
+        old = {"parentGuardian": {"email": "old@example.com"}}
+        new = {"parentGuardian": {"email": "new@example.com"}}
+        diff = _diff_registrations(old, new)
+        assert "parentGuardian.email" in diff
+
+
+# ---------------------------------------------------------------------------
+# ConversationStore — CRUD
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def store(tmp_path) -> ConversationStore:
+    return ConversationStore(tmp_path)
+
+
+class TestConversationStoreCRUD:
+    def test_load_returns_none_for_unknown_email(self, store):
+        assert store.load("nobody@example.com") is None
+
+    def test_save_and_load_round_trip(self, store, fresh_state):
+        store.save(fresh_state)
+        loaded = store.load(fresh_state.parent_email)
+        assert loaded is not None
+        assert loaded.conversation_id == fresh_state.conversation_id
+
+    def test_save_overwrites_existing(self, store, fresh_state):
+        store.save(fresh_state)
+        fresh_state.language = "en"
+        store.save(fresh_state)
+        loaded = store.load(fresh_state.parent_email)
+        assert loaded.language == "en"
+
+    def test_delete_removes_conversation(self, store, fresh_state):
+        store.save(fresh_state)
+        store.delete(fresh_state.parent_email)
+        assert store.load(fresh_state.parent_email) is None
+
+    def test_delete_nonexistent_is_silent(self, store):
+        store.delete("ghost@example.com")  # should not raise
+
+    def test_list_incomplete_returns_non_completed(self, store, fresh_state):
+        store.save(fresh_state)
+        incomplete = store.list_incomplete()
+        assert any(s.conversation_id == fresh_state.conversation_id for s in incomplete)
+
+    def test_list_incomplete_excludes_completed(self, store, fresh_state):
+        fresh_state.completed = True
+        store.save(fresh_state)
+        incomplete = store.list_incomplete()
+        assert all(not s.completed for s in incomplete)
+
+    def test_find_by_email_is_alias_for_load(self, store, fresh_state):
+        store.save(fresh_state)
+        assert store.find_by_email(fresh_state.parent_email) is not None
+
+
+# ---------------------------------------------------------------------------
+# ConversationStore — registration versioning
+# ---------------------------------------------------------------------------
+
+
+class TestRegistrationVersioning:
+    def test_save_registration_creates_version_1(self, store, fresh_state, complete_registration):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        email_key, version = store.save_registration(fresh_state)
+        assert version == 1
+        # email_key is the filesystem-safe form (@ → _at_)
+        assert email_key == "anna.muster_at_example.com"
+
+    def test_save_registration_writes_current_json(self, store, fresh_state, complete_registration, tmp_path):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        email_key, _ = store.save_registration(fresh_state)
+        current = tmp_path / "registrations" / email_key / "current.json"
+        assert current.exists()
+
+    def test_save_registration_version_increments(self, store, fresh_state, complete_registration):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        store.save_registration(fresh_state)
+        _, v2 = store.save_registration_version(
+            fresh_state, {"child.fullName": ("Old", "New")}
+        )
+        assert v2 == 2
+
+    def test_get_current_registration_returns_latest(self, store, fresh_state, complete_registration):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        store.save_registration(fresh_state)
+        current = store.get_current_registration(fresh_state.parent_email)
+        assert current is not None
+        assert current["metadata"]["version"] == 1
+
+    def test_get_registration_history_returns_all_versions(self, store, fresh_state, complete_registration):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        store.save_registration(fresh_state)
+        store.save_registration_version(fresh_state, {"child.fullName": ("A", "B")})
+        history = store.get_registration_history(fresh_state.parent_email)
+        assert len(history) == 2
+
+    def test_list_registrations_includes_saved(self, store, fresh_state, complete_registration):
+        fresh_state.registration = complete_registration
+        fresh_state.completed = True
+        store.save_registration(fresh_state)
+        registrations = store.list_registrations()
+        assert len(registrations) == 1