diff --git a/git_commit_ai/tests/test_conventional.py b/git_commit_ai/tests/test_conventional.py
new file mode 100644
index 0000000..92c00eb
--- /dev/null
+++ b/git_commit_ai/tests/test_conventional.py
@@ -0,0 +1,131 @@
+"""Tests for conventional commit validation."""
+
+import pytest
+
+from git_commit_ai.core.conventional import (
+    ConventionalCommitParser,
+    ConventionalCommitFixer,
+    validate_commit_message,
+    format_conventional,
+    extract_conventional_parts,
+)
+
+
+class TestConventionalCommitParser:
+    """Tests for ConventionalCommitParser."""
+
+    def test_parse_valid_message(self):
+        message = "feat(auth): add user authentication"
+        parsed = ConventionalCommitParser.parse(message)
+        assert parsed is not None
+        assert parsed.type == "feat"
+        assert parsed.scope == "auth"
+        assert parsed.description == "add user authentication"
+
+    def test_parse_without_scope(self):
+        message = "fix: resolve memory leak"
+        parsed = ConventionalCommitParser.parse(message)
+        assert parsed is not None
+        assert parsed.type == "fix"
+        assert parsed.scope is None
+
+    def test_parse_invalid_message(self):
+        message = "just a random message"
+        parsed = ConventionalCommitParser.parse(message)
+        assert parsed is None
+
+    def test_is_valid(self):
+        assert ConventionalCommitParser.is_valid("feat: new feature") is True
+        assert ConventionalCommitParser.is_valid("invalid message") is False
+
+    def test_validate_valid(self):
+        errors = ConventionalCommitParser.validate("feat(auth): add login")
+        assert len(errors) == 0
+
+    def test_validate_invalid_type(self):
+        errors = ConventionalCommitParser.validate("invalid(scope): desc")
+        assert len(errors) > 0
+        assert any("Invalid type" in e for e in errors)
+
+    def test_validate_empty_message(self):
+        errors = ConventionalCommitParser.validate("")
+        assert len(errors) > 0
+
+
+class TestConventionalCommitFixer:
+    """Tests for ConventionalCommitFixer."""
+
+    def test_fix_simple_message(self):
+        diff = """+++ b/src/auth.py
+@@ -1,3 +1,4 @@
++def login():
++    pass
+"""
+        fixed = ConventionalCommitFixer.fix("add login feature", diff)
+        assert fixed.startswith("feat:")
+
+    def test_fix_with_type_detection(self):
+        diff = """--- a/src/bug.py
++++ b/src/bug.py
+@@ -1,3 +1,4 @@
+-def calculate():
++def calculate():
+     return 1 / 0
++    return 1 / 1
+"""
+        fixed = ConventionalCommitFixer.fix("fix bug", diff)
+        assert fixed.startswith("fix:")
+
+    def test_fix_preserves_description(self):
+        diff = """+++ b/src/auth.py
+@@ -1,3 +1,4 @@
++def login():
+"""
+        fixed = ConventionalCommitFixer.fix("add login functionality", diff)
+        assert "login" in fixed.lower()
+
+
+class TestValidateCommitMessage:
+    """Tests for validate_commit_message function."""
+
+    def test_validate_valid(self):
+        is_valid, errors = validate_commit_message("feat(auth): add login")
+        assert is_valid is True
+        assert len(errors) == 0
+
+    def test_validate_invalid(self):
+        is_valid, errors = validate_commit_message("invalid")
+        assert is_valid is False
+        assert len(errors) > 0
+
+
+class TestFormatConventional:
+    """Tests for format_conventional function."""
+
+    def test_format_with_type_and_scope(self):
+        result = format_conventional("add login", "feat", "auth")
+        assert result == "feat(auth): add login"
+
+    def test_format_with_type_only(self):
+        result = format_conventional("fix bug", "fix")
+        assert result == "fix: fix bug"
+
+    def test_format_already_formatted(self):
+        result = format_conventional("feat(auth): add login", "feat", "auth")
+        assert result == "feat(auth): add login"
+
+
+class TestExtractConventionalParts:
+    """Tests for extract_conventional_parts function."""
+
+    def test_extract_all_parts(self):
+        result = extract_conventional_parts("feat(auth): add login")
+        assert result["type"] == "feat"
+        assert result["scope"] == "auth"
+        assert result["description"] == "add login"
+
+    def test_extract_invalid_message(self):
+        result = extract_conventional_parts("invalid message")
+        assert result["type"] is None
+        assert result["scope"] is None
+        assert result["description"] == "invalid message"