diff --git a/tests/test_detector.py b/tests/test_detector.py
new file mode 100644
index 0000000..0c189b3
--- /dev/null
+++ b/tests/test_detector.py
@@ -0,0 +1,136 @@
+"""Tests for detector.py."""
+
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from gitignore_generator.detector import (
+    ProjectDetector,
+    detect_project,
+    suggest_gitignore,
+    DETECTION_RULES
+)
+
+
+class TestProjectDetector:
+    """Tests for ProjectDetector class."""
+
+    @pytest.fixture
+    def detector(self):
+        """Create detector with temp directory."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            yield ProjectDetector(Path(tmpdir))
+
+    def test_detect_node_project(self, detector):
+        """Test detecting Node.js project."""
+        (detector.path / 'package.json').touch()
+        (detector.path / 'node_modules').mkdir()
+
+        result = detector.detect()
+        assert 'node' in result
+
+    def test_detect_python_project(self, detector):
+        """Test detecting Python project."""
+        (detector.path / 'requirements.txt').touch()
+        (detector.path / 'venv').mkdir()
+
+        result = detector.detect()
+        assert 'python' in result
+
+    def test_detect_django_project(self, detector):
+        """Test detecting Django project."""
+        (detector.path / 'manage.py').touch()
+        (detector.path / 'settings.py').touch()
+
+        result = detector.detect()
+        assert 'django' in result
+
+    def test_detect_multiple_technologies(self, detector):
+        """Test detecting multiple technologies."""
+        (detector.path / 'package.json').touch()
+        (detector.path / 'requirements.txt').touch()
+        (detector.path / 'Dockerfile').touch()
+
+        result = detector.detect()
+        assert 'node' in result
+        assert 'python' in result
+        assert 'docker' in result
+
+    def test_detect_no_project(self, detector):
+        """Test when no project is detected."""
+        result = detector.detect()
+        assert len(result) == 0
+
+    def test_detect_with_min_confidence(self, detector):
+        """Test minimum confidence threshold."""
+        (detector.path / 'package.json').touch()
+
+        result = detector.detect(min_confidence=2)
+        assert 'node' not in result
+
+    def test_get_detection_details(self, detector):
+        """Test getting detailed detection results."""
+        (detector.path / 'package.json').touch()
+        (detector.path / 'yarn.lock').touch()
+
+        details = detector.get_detection_details()
+        assert len(details) > 0
+        assert details[0]['technology'] == 'node'
+        assert details[0]['confidence'] >= 1
+
+    def test_suggest_gitignore(self, detector):
+        """Test gitignore suggestions."""
+        (detector.path / 'package.json').touch()
+        (detector.path / 'requirements.txt').touch()
+        (detector.path / 'manage.py').touch()
+
+        suggestions = detector.suggest_gitignore()
+        assert 'node' in suggestions
+        assert 'python' in suggestions
+        assert 'django' in suggestions
+
+    def test_scan_directory(self, detector):
+        """Test directory scanning."""
+        (detector.path / 'package.json').touch()
+        (detector.path / 'requirements.txt').touch()
+
+        result = detector.scan_directory()
+        assert 'node' in result
+        assert 'python' in result
+
+
+class TestDetectionRules:
+    """Tests for detection rules configuration."""
+
+    def test_detection_rules_exist(self):
+        """Test that detection rules are defined."""
+        assert len(DETECTION_RULES) > 0
+
+    def test_common_technologies_have_rules(self):
+        """Test that common technologies have detection rules."""
+        common = ['node', 'python', 'django', 'rails', 'java', 'go', 'rust', 'dotnet']
+        for tech in common:
+            assert tech in DETECTION_RULES
+            assert len(DETECTION_RULES[tech]) > 0
+
+    def test_each_rule_has_markers(self):
+        """Test that each detection rule has markers."""
+        for tech, markers in DETECTION_RULES.items():
+            assert len(markers) > 0, f"{tech} has no markers"
+
+
+class TestConvenienceFunctions:
+    """Tests for convenience functions."""
+
+    def test_detect_project_function(self, detector):
+        """Test detect_project convenience function."""
+        (detector.path / 'requirements.txt').touch()
+        result = detect_project(detector.path)
+        assert 'python' in result
+
+    def test_suggest_gitignore_function(self, detector):
+        """Test suggest_gitignore convenience function."""
+        (detector.path / 'requirements.txt').touch()
+        result = suggest_gitignore(detector.path)
+        assert 'python' in result