diff --git a/tests/test_extract.py b/tests/test_extract.py
new file mode 100644
index 0000000..a81cc45
--- /dev/null
+++ b/tests/test_extract.py
@@ -0,0 +1,149 @@
+"""Tests for key extraction module."""
+import tempfile
+from pathlib import Path
+
+from i18n_key_sync.extract import ExtractKeys, extract_keys
+
+
+class TestExtractKeys:
+    """Tests for ExtractKeys class."""
+
+    def test_extract_simple_keys(self, sample_python_code):
+        """Test extracting simple i18n keys from Python code."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write(sample_python_code)
+            f.flush()
+
+            extractor = ExtractKeys(["_", "t"])
+            keys = extractor.extract_from_file(Path(f.name))
+
+            assert "hello" in keys
+            assert "goodbye" in keys
+            assert "welcome_message" in keys
+            assert "save" in keys
+            assert "cancel" in keys
+
+            Path(f.name).unlink()
+
+    def test_extract_js_keys(self, sample_js_code):
+        """Test extracting keys from JavaScript code."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".js", delete=False) as f:
+            f.write(sample_js_code)
+            f.flush()
+
+            extractor = ExtractKeys(["_", "t", "i18n.t"])
+            keys = extractor.extract_from_file(Path(f.name))
+
+            assert "hello_world" in keys
+            assert "greeting" in keys
+            assert "welcome_message" in keys
+            assert "submit" in keys
+
+            Path(f.name).unlink()
+
+    def test_extract_multiple_patterns(self):
+        """Test extracting keys using multiple patterns."""
+        code = '''
+_("key1")
+t("key2")
+i18n.t("key3")
+gettext("key4")
+'''
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write(code)
+            f.flush()
+
+            extractor = ExtractKeys(["_", "t", "i18n.t", "gettext"])
+            keys = extractor.extract_from_file(Path(f.name))
+
+            assert keys == {"key1", "key2", "key3", "key4"}
+
+            Path(f.name).unlink()
+
+    def test_extract_template_literals(self):
+        """Test extracting keys from template literals."""
+        code = '''
+const greeting = `Hello ${_("user_name")}, ${_("welcome_message")}`;
+'''
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".js", delete=False) as f:
+            f.write(code)
+            f.flush()
+
+            extractor = ExtractKeys(["_"])
+            keys = extractor.extract_from_file(Path(f.name))
+
+            assert "user_name" in keys
+            assert "welcome_message" in keys
+
+            Path(f.name).unlink()
+
+    def test_extract_no_keys(self):
+        """Test extracting from code with no i18n calls."""
+        code = '''
+def hello(name):
+    return "Hello " + name
+'''
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write(code)
+            f.flush()
+
+            extractor = ExtractKeys(["_", "t"])
+            keys = extractor.extract_from_file(Path(f.name))
+
+            assert keys == set()
+
+            Path(f.name).unlink()
+
+    def test_extract_from_files(self):
+        """Test extracting keys from multiple files."""
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f1:
+            f1.write('_("key1")\n_("key2")')
+            f1_path = Path(f1.name)
+
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".js", delete=False) as f2:
+            f2.write('t("key3")\nt("key4")')
+            f2_path = Path(f2.name)
+
+        try:
+            extractor = ExtractKeys(["_", "t"])
+            keys = extractor.extract_from_files([f1_path, f2_path])
+
+            assert keys == {"key1", "key2", "key3", "key4"}
+        finally:
+            f1_path.unlink()
+            f2_path.unlink()
+
+
+class TestExtractKeysFunction:
+    """Tests for the extract_keys function."""
+
+    def test_extract_keys_from_directory(self, temp_project_dir):
+        """Test extracting keys from a directory."""
+        paths = (str(temp_project_dir / "src"),)
+        patterns = ["_", "t", "i18n.t"]
+        file_types = ["py", "js"]
+
+        keys = extract_keys(paths, patterns, file_types)
+
+        assert len(keys) > 0
+        assert "hello" in keys or "hello_world" in keys
+
+    def test_extract_keys_with_file_types_filter(self, temp_project_dir):
+        """Test extracting keys with file type filtering."""
+        paths = (str(temp_project_dir / "src"),)
+        patterns = ["_", "t"]
+        file_types = ["py"]
+
+        keys = extract_keys(paths, patterns, file_types)
+
+        assert "goodbye" in keys
+
+    def test_extract_keys_nonexistent_path(self):
+        """Test extracting from nonexistent path returns empty set."""
+        paths = ("/nonexistent/path",)
+        patterns = ["_", "t"]
+        file_types = ["py"]
+
+        keys = extract_keys(paths, patterns, file_types)
+
+        assert keys == set()