Add comprehensive test suite for MVP-1 Personal Tracker CLI

Implements 72 tests covering:
- Model tests (Project, Session, Note, Change)
- ProjectService tests (create, get, list, ensure structure)
- SessionService tests (active session management)
- FileStorage tests (read/write operations)
- Complete flow tests (init -> start -> note -> stop -> show)
- Note consolidation tests

Uses pytest with tmp_path fixtures for isolated testing.

tests/test_session_service.py

@@ -0,0 +1,241 @@
+"""Tests for SessionService."""
+
+import json
+from datetime import datetime
+from pathlib import Path
+from unittest.mock import patch, MagicMock
+
+import pytest
+
+from tracker.models import Session
+from tracker.services import (
+    get_active_session,
+    set_active_session,
+    clear_active_session,
+    get_active_session_path,
+    validate_no_other_active_session,
+)
+
+
+@pytest.fixture
+def mock_active_session_path(tmp_path, monkeypatch):
+    """Mock the active session path to use tmp_path."""
+    fake_path = tmp_path / ".active_session.json"
+
+    def mock_get_active_session_path():
+        return fake_path
+
+    monkeypatch.setattr(
+        "tracker.services.session_service.get_active_session_path",
+        mock_get_active_session_path
+    )
+    return fake_path
+
+
+class TestSetAndGetActiveSession:
+    """Tests for set and get active session functions."""
+
+    def test_set_and_get_active_session(self, tmp_path, mock_session, monkeypatch):
+        """Test setting and getting an active session."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+        retrieved = get_active_session()
+
+        assert retrieved is not None
+        assert retrieved.id == mock_session.id
+        assert retrieved.project_slug == mock_session.project_slug
+        assert retrieved.started_at == mock_session.started_at
+
+    def test_get_active_session_returns_none_when_no_session(self, tmp_path, monkeypatch):
+        """Test that get_active_session returns None when no session exists."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        result = get_active_session()
+        assert result is None
+
+    def test_set_active_session_creates_parent_directories(self, tmp_path, mock_session, monkeypatch):
+        """Test that set_active_session creates parent directories if needed."""
+        fake_path = tmp_path / "subdir" / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+        assert fake_path.exists()
+
+    def test_active_session_contains_all_fields(self, tmp_path, mock_session, monkeypatch):
+        """Test that active session file contains all session fields."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+
+        with open(fake_path, "r") as f:
+            data = json.load(f)
+
+        assert data["id"] == mock_session.id
+        assert data["project_slug"] == mock_session.project_slug
+        assert "started_at" in data
+        assert "work_done" in data
+        assert data["work_done"] == mock_session.work_done
+
+
+class TestClearActiveSession:
+    """Tests for clear_active_session function."""
+
+    def test_clear_active_session_removes_file(self, tmp_path, mock_session, monkeypatch):
+        """Test that clear_active_session removes the active session file."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+        assert fake_path.exists()
+
+        clear_active_session()
+        assert not fake_path.exists()
+
+    def test_clear_active_session_when_no_session(self, tmp_path, monkeypatch):
+        """Test that clear_active_session does not error when no session exists."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        clear_active_session()
+        assert not fake_path.exists()
+
+    def test_get_active_session_after_clear(self, tmp_path, mock_session, monkeypatch):
+        """Test that get_active_session returns None after clearing."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+        clear_active_session()
+
+        result = get_active_session()
+        assert result is None
+
+
+class TestValidateNoOtherActiveSession:
+    """Tests for validate_no_other_active_session function."""
+
+    def test_validate_no_other_active_session_returns_true_when_none(self, tmp_path, monkeypatch):
+        """Test validation returns True when no active session exists."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        result = validate_no_other_active_session("any-project")
+        assert result is True
+
+    def test_validate_no_other_active_session_returns_true_for_same_project(
+        self, tmp_path, mock_session, monkeypatch
+    ):
+        """Test validation returns True for same project's session."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+
+        result = validate_no_other_active_session(mock_session.project_slug)
+        assert result is True
+
+    def test_validate_no_other_active_session_returns_false_for_different_project(
+        self, tmp_path, mock_session, monkeypatch
+    ):
+        """Test validation returns False for different project's session."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+
+        result = validate_no_other_active_session("different-project")
+        assert result is False
+
+    def test_validate_no_other_active_session_with_no_active_after_clear(
+        self, tmp_path, mock_session, monkeypatch
+    ):
+        """Test validation returns True after clearing session."""
+        fake_path = tmp_path / ".active_session.json"
+
+        def mock_get_active_session_path():
+            return fake_path
+
+        monkeypatch.setattr(
+            "tracker.services.session_service.get_active_session_path",
+            mock_get_active_session_path
+        )
+
+        set_active_session(mock_session)
+        clear_active_session()
+
+        result = validate_no_other_active_session("any-project")
+        assert result is True