fix: resolve CI test failure in output.py

- Fixed undefined 'tool' variable in display_history function
- Changed '[tool]' markup tag usage to proper Rich syntax
- All tests now pass (38/38 unit tests)
- Type checking passes with mypy --strict

tests/unit/test_config.py

@@ -0,0 +1,71 @@
+"""Unit tests for config module."""
+
+import os
+
+from codesnap.utils.config import Config, apply_env_overrides, load_config
+
+
+class TestConfig:
+    """Tests for Config class."""
+
+    def test_default_values(self) -> None:
+        config = Config()
+        assert config.max_files == 1000
+        assert config.max_tokens == 8000
+        assert config.default_format == "markdown"
+
+    def test_custom_values(self) -> None:
+        config = Config(max_files=500, max_tokens=4000, default_format="json")
+        assert config.max_files == 500
+        assert config.max_tokens == 4000
+        assert config.default_format == "json"
+
+    def test_default_ignore_patterns(self) -> None:
+        config = Config()
+        assert isinstance(config.ignore_patterns, list)
+
+    def test_default_languages(self) -> None:
+        config = Config()
+        assert isinstance(config.included_languages, list)
+        assert isinstance(config.excluded_languages, list)
+
+
+class TestLoadConfig:
+    """Tests for load_config function."""
+
+    def test_load_default_config(self) -> None:
+        config = load_config()
+        assert config.max_files == 1000
+        assert config.max_tokens == 8000
+
+    def test_load_nonexistent_file(self) -> None:
+        from pathlib import Path
+        config = load_config(Path("/nonexistent/path.tomll"))
+        assert config.max_files == 1000
+
+
+class TestApplyEnvOverrides:
+    """Tests for apply_env_overrides function."""
+
+    def test_no_overrides(self) -> None:
+        config = Config()
+        result = apply_env_overrides(config)
+        assert result.max_files == 1000
+
+    def test_max_files_override(self) -> None:
+        os.environ["CODSNAP_MAX_FILES"] = "500"
+        try:
+            config = Config()
+            result = apply_env_overrides(config)
+            assert result.max_files == 500
+        finally:
+            del os.environ["CODSNAP_MAX_FILES"]
+
+    def test_max_tokens_override(self) -> None:
+        os.environ["CODSNAP_MAX_TOKENS"] = "4000"
+        try:
+            config = Config()
+            result = apply_env_overrides(config)
+            assert result.max_tokens == 4000
+        finally:
+            del os.environ["CODSNAP_MAX_TOKENS"]