diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..f4ed619
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,135 @@
+"""Pytest configuration and fixtures."""
+import json
+
+import pytest
+
+from i18n_key_sync.locale import LocaleParser
+
+
+@pytest.fixture
+def sample_python_code():
+    """Sample Python code with i18n keys."""
+    return '''
+from gettext import gettext as _
+
+def greet(name):
+    return _("hello") + " " + name
+
+def farewell():
+    return _("goodbye")
+
+messages = {
+    "welcome": _("welcome_message"),
+    "login": t("login_button"),
+}
+
+
+# Inline usage
+print(_("save"))
+print(_("cancel"))
+'''
+
+
+@pytest.fixture
+def sample_js_code():
+    """Sample JavaScript code with i18n keys."""
+    return '''
+import { t } from './i18n';
+
+const message = _("hello_world");
+const greeting = t("greeting");
+
+function showWelcome() {
+    return i18n.t("welcome_message");
+}
+
+// Template usage
+const text = `Hello ${name}, ${_("welcome_message")}`;
+
+// JSX usage
+return <div>{_("submit")}</div>;
+'''
+
+
+@pytest.fixture
+def sample_locale_json():
+    """Sample JSON locale file."""
+    return {
+        "hello": "Hello",
+        "goodbye": "Goodbye",
+        "welcome_message": "Welcome!",
+        "save": "Save",
+        "cancel": "Cancel",
+        "unused_key": "This key is not used",
+    }
+
+
+@pytest.fixture
+def sample_locale_yaml():
+    """Sample YAML locale file."""
+    return {
+        "hello": "Hello",
+        "goodbye": "Goodbye",
+        "welcome_message": "Welcome!",
+        "save": "Save",
+        "cancel": "Cancel",
+        "unused_key": "This key is not used",
+        "nested": {
+            "key": "Nested value",
+            "deep": {
+                "key": "Deep nested value",
+            },
+        },
+    }
+
+
+@pytest.fixture
+def temp_locale_dir(tmp_path, sample_locale_json):
+    """Create a temporary locale directory with sample files."""
+    locale_dir = tmp_path / "locales"
+    locale_dir.mkdir()
+
+    en_file = locale_dir / "en.json"
+    en_file.write_text(json.dumps(sample_locale_json, indent=2))
+
+    es_file = locale_dir / "es.json"
+    es_data = sample_locale_json.copy()
+    es_data["hello"] = "Hola"
+    es_file.write_text(json.dumps(es_data, indent=2))
+
+    return locale_dir
+
+
+@pytest.fixture
+def temp_locale_dir_yaml(tmp_path, sample_locale_yaml):
+    """Create a temporary locale directory with YAML files."""
+    import yaml
+
+    locale_dir = tmp_path / "locales_yaml"
+    locale_dir.mkdir()
+
+    en_file = locale_dir / "en.yaml"
+    en_file.write_text(yaml.dump(sample_locale_yaml, default_flow_style=False))
+
+    return locale_dir
+
+
+@pytest.fixture
+def locale_parser():
+    """Create a LocaleParser instance."""
+    return LocaleParser()
+
+
+@pytest.fixture
+def temp_project_dir(tmp_path, sample_python_code, sample_js_code, temp_locale_dir):
+    """Create a temporary project directory with code and locales."""
+    src_dir = tmp_path / "src"
+    src_dir.mkdir()
+
+    python_file = src_dir / "main.py"
+    python_file.write_text(sample_python_code)
+
+    js_file = src_dir / "app.js"
+    js_file.write_text(sample_js_code)
+
+    return tmp_path