diff --git a/tests/unit/test_language_detector.py b/tests/unit/test_language_detector.py
new file mode 100644
index 0000000..553d998
--- /dev/null
+++ b/tests/unit/test_language_detector.py
@@ -0,0 +1,168 @@
+"""Unit tests for language detection module."""
+
+from pathlib import Path
+
+from codesnap.core.language_detector import (
+    EXTENSION_TO_LANGUAGE,
+    detect_language,
+    detect_language_by_extension,
+    detect_language_by_shebang,
+    get_language_info,
+    get_supported_extensions,
+    get_supported_languages,
+)
+
+
+class TestDetectLanguageByExtension:
+    """Tests for extension-based language detection."""
+
+    def test_python_extension_py(self):
+        assert detect_language_by_extension(Path("test.py")) == "python"
+
+    def test_python_extension_pyi(self):
+        assert detect_language_by_extension(Path("test.pyi")) == "python"
+
+    def test_javascript_extension_js(self):
+        assert detect_language_by_extension(Path("test.js")) == "javascript"
+
+    def test_typescript_extension_ts(self):
+        assert detect_language_by_extension(Path("test.ts")) == "typescript"
+
+    def test_go_extension(self):
+        assert detect_language_by_extension(Path("main.go")) == "go"
+
+    def test_rust_extension(self):
+        assert detect_language_by_extension(Path("main.rs")) == "rust"
+
+    def test_java_extension(self):
+        assert detect_language_by_extension(Path("Main.java")) == "java"
+
+    def test_cpp_extension(self):
+        assert detect_language_by_extension(Path("test.cpp")) == "cpp"
+        assert detect_language_by_extension(Path("test.hpp")) == "cpp"
+
+    def test_ruby_extension(self):
+        assert detect_language_by_extension(Path("script.rb")) == "ruby"
+
+    def test_php_extension(self):
+        assert detect_language_by_extension(Path("script.php")) == "php"
+
+    def test_unknown_extension(self):
+        assert detect_language_by_extension(Path("test.xyz")) is None
+
+    def test_case_insensitive(self):
+        assert detect_language_by_extension(Path("test.PY")) == "python"
+        assert detect_language_by_extension(Path("test.JS")) == "javascript"
+
+
+class TestDetectLanguageByShebang:
+    """Tests for shebang-based language detection."""
+
+    def test_python_shebang(self):
+        content = "#!/usr/bin/env python3\nprint('hello')"
+        assert detect_language_by_shebang(content) == "python"
+
+    def test_python_shebang_alt(self):
+        content = "#!/usr/bin/env python\nprint('hello')"
+        assert detect_language_by_shebang(content) == "python"
+
+    def test_node_shebang(self):
+        content = "#!/usr/bin/env node\nconsole.log('hello')"
+        assert detect_language_by_shebang(content) == "javascript"
+
+    def test_ruby_shebang(self):
+        content = "#!/usr/bin/env ruby\nputs 'hello'"
+        assert detect_language_by_shebang(content) == "ruby"
+
+    def test_php_shebang(self):
+        content = "#!/usr/bin/env php\necho 'hello';"
+        assert detect_language_by_shebang(content) == "php"
+
+    def test_no_shebang(self):
+        content = "print('hello')"
+        assert detect_language_by_shebang(content) is None
+
+    def test_empty_content(self):
+        assert detect_language_by_shebang("") is None
+
+
+class TestDetectLanguage:
+    """Tests for combined language detection."""
+
+    def test_detection_by_extension(self):
+        assert detect_language(Path("test.py")) == "python"
+        assert detect_language(Path("test.js")) == "javascript"
+
+    def test_detection_fallback_to_shebang(self):
+        file_path = Path("script")
+        assert detect_language(file_path, "#!/usr/bin/env python") == "python"
+        assert detect_language(file_path, "#!/usr/bin/env node") == "javascript"
+
+    def test_unknown_file_no_content(self):
+        assert detect_language(Path("unknown.xyz")) is None
+
+
+class TestGetLanguageInfo:
+    """Tests for language info retrieval."""
+
+    def test_get_python_info(self):
+        info = get_language_info("python")
+        assert info is not None
+        assert info.name == "python"
+        assert ".py" in info.extensions
+
+    def test_get_unknown_language(self):
+        info = get_language_info("unknown")
+        assert info is None
+
+
+class TestGetSupportedExtensions:
+    """Tests for supported extensions."""
+
+    def test_returns_set(self):
+        extensions = get_supported_extensions()
+        assert isinstance(extensions, set)
+
+    def test_includes_common_extensions(self):
+        extensions = get_supported_extensions()
+        assert ".py" in extensions
+        assert ".js" in extensions
+        assert ".ts" in extensions
+        assert ".go" in extensions
+
+
+class TestGetSupportedLanguages:
+    """Tests for supported programming languages."""
+
+    def test_returns_list(self):
+        languages = get_supported_languages()
+        assert isinstance(languages, list)
+
+    def test_includes_main_languages(self):
+        languages = get_supported_languages()
+        assert "python" in languages
+        assert "javascript" in languages
+        assert "typescript" in languages
+        assert "go" in languages
+        assert "rust" in languages
+        assert "java" in languages
+
+    def test_excludes_config_formats(self):
+        languages = get_supported_languages()
+        assert "json" not in languages
+        assert "yaml" not in languages
+        assert "markdown" not in languages
+
+
+class TestExtensionToLanguage:
+    """Tests for extension to language mapping."""
+
+    def test_mapping_completeness(self):
+        for _ext, lang in EXTENSION_TO_LANGUAGE.items():
+            assert lang in ["python", "javascript", "typescript", "go", "rust",
+                           "java", "c", "cpp", "ruby", "php", "shell",
+                           "json", "yaml", "markdown"]
+
+    def test_no_duplicate_extensions(self):
+        extensions = list(EXTENSION_TO_LANGUAGE.keys())
+        assert len(extensions) == len(set(extensions))