diff --git a/tests/test_checker.py b/tests/test_checker.py
index 1f32c0d..a04d68b 100644
--- a/tests/test_checker.py
+++ b/tests/test_checker.py
@@ -79,6 +79,12 @@ def test_check_filename_empty():
     assert "empty name" in error
 
 
+def test_check_filename_none():
+    """Test check_filename with None"""
+    error = checker.check_filename(None)
+    assert "empty name" in error
+
+
 # ============================================================================
 # check_kind tests
 # ============================================================================
@@ -110,6 +116,21 @@ def test_check_kind_symlink(tmp_path):
     assert checker.check_kind(str(link), follow_symlink=False) == "symlink"
 
 
+def test_check_kind_special_files(tmp_path):
+    """Test check_kind with special file types"""
+    special_files = {
+        "char_device": 0o020666,  # S_IFCHR
+        "block_device": 0o060666,  # S_IFBLK
+        "socket": 0o140666,  # S_IFSOCK
+        "fifo": 0o010666,  # S_IFIFO
+    }
+
+    for kind, mode in special_files.items():
+        with patch("os.stat") as mock_stat:
+            mock_stat.return_value = MagicMock(st_mode=mode)
+            assert checker.check_kind("fake_path") == kind
+
+
 # ============================================================================
 # check_daemon tests
 # ============================================================================
@@ -352,6 +373,34 @@ def test_validate_time_field_logic_range_out_of_bounds_end():
     assert any("range end" in e and "out of bounds" in e for e in errors)
 
 
+def test_validate_time_field_logic_duplicate_value():
+    """Test validate_time_field_logic with duplicate values in a list"""
+    errors = checker.validate_time_field_logic("1,2,1", "minutes", 0, 59)
+    assert len(errors) > 0
+    assert any("duplicate value" in e for e in errors)
+
+
+def test_validate_time_field_logic_empty_value():
+    """Test validate_time_field_logic with an empty value in a list"""
+    errors = checker.validate_time_field_logic("1,,2", "minutes", 0, 59)
+    assert len(errors) > 0
+    assert any("empty value" in e for e in errors)
+
+
+def test_validate_time_field_logic_invalid_step_format():
+    """Test validate_time_field_logic with an invalid step format"""
+    errors = checker.validate_time_field_logic("*/a", "minutes", 0, 59)
+    assert len(errors) > 0
+    assert any("invalid step value" in e for e in errors)
+
+
+def test_validate_time_field_logic_invalid_range():
+    """Test validate_time_field_logic with an invalid range where start > end"""
+    errors = checker.validate_time_field_logic("5-1", "minutes", 0, 59)
+    assert len(errors) > 0
+    assert any("invalid range" in e for e in errors)
+
+
 # ============================================================================
 # check_user_exists tests
 # ============================================================================
@@ -435,6 +484,56 @@ def test_check_command_missing():
     assert "missing command" in errors[0]
 
 
+def test_check_dangerous_commands():
+    """Test check_dangerous_commands with dangerous commands"""
+    dangerous_commands = [
+        "rm -rf /",
+        "rm -rf /root",
+        "rm -rf / && ls",
+        "rm -rf / || ls",
+        "rm -rf / ; ls",
+    ]
+    for command in dangerous_commands:
+        errors = checker.check_dangerous_commands(command)
+        assert len(errors) > 0
+        assert any("dangerous command" in e for e in errors)
+
+
+def test_check_minutes_invalid_format():
+    """Test check_minutes with an invalid format"""
+    errors = checker.check_minutes("a", is_system_crontab=False)
+    assert len(errors) > 0
+    assert any("invalid minute format" in e for e in errors)
+
+
+def test_check_hours_invalid_format():
+    """Test check_hours with an invalid format"""
+    errors = checker.check_hours("a")
+    assert len(errors) > 0
+    assert any("invalid hour format" in e for e in errors)
+
+
+def test_check_day_of_month_invalid_format():
+    """Test check_day_of_month with an invalid format"""
+    errors = checker.check_day_of_month("a")
+    assert len(errors) > 0
+    assert any("invalid day of month format" in e for e in errors)
+
+
+def test_check_month_invalid_format():
+    """Test check_month with an invalid format"""
+    errors = checker.check_month("a")
+    assert len(errors) > 0
+    assert any("invalid month format" in e for e in errors)
+
+
+def test_check_day_of_week_invalid_format():
+    """Test check_day_of_week with an invalid format"""
+    errors = checker.check_day_of_week("a")
+    assert len(errors) > 0
+    assert any("invalid day of week format" in e for e in errors)
+
+
 # ============================================================================
 # Legacy functions tests
 # ============================================================================
@@ -463,6 +562,32 @@ def test_check_line_special_legacy():
 # ============================================================================
 
 
+def test_check_line_insufficient_fields_special():
+    """Test check_line with insufficient fields for a special keyword"""
+    errors, warnings = checker.check_line("@reboot", 1, "test.txt")
+    assert len(errors) > 0
+    assert any("insufficient fields" in e for e in errors)
+
+
+def test_check_line_insufficient_fields_regular():
+    """Test check_line with insufficient fields for a regular crontab line"""
+    errors, warnings = checker.check_line("* * * *", 1, "test.txt")
+    assert len(errors) > 0
+    assert any("insufficient fields" in e for e in errors)
+
+
+def test_check_line_system_extra_field_in_command():
+    """Test check_line with an extra field in the command for a system crontab line"""
+    errors, warnings = checker.check_line(
+        "* * * * * root extra /usr/bin/backup.sh",
+        1,
+        "test.txt",
+        is_system_crontab=True,
+    )
+    assert len(errors) > 0
+    assert any("extra field" in e for e in errors)
+
+
 @patch("checkcrontab.checker.os.lstat")
 @patch("checkcrontab.checker.os.path.exists")
 @patch("checkcrontab.checker.os.path.lexists")
@@ -558,6 +683,31 @@ def test_check_line_multiline_continuation_with_backslash():
     pass  # Will test through integration tests
 
 
+def test_check_user_invalid_format():
+    """Test check_user with various invalid formats"""
+    invalid_usernames = ["", "#user", '"user"', "user@", "user name", "-user"]
+    for username in invalid_usernames:
+        errors, warnings = checker.check_user(username)
+        assert len(errors) > 0
+        assert any("invalid user format" in e for e in errors)
+
+
+def test_check_special_invalid_keyword():
+    """Test check_special with an invalid keyword"""
+    errors = checker.check_special(
+        "@invalid", ["@invalid", "command"], is_system_crontab=False
+    )
+    assert len(errors) > 0
+    assert any("invalid special keyword" in e for e in errors)
+
+
+def test_check_line_with_env_var():
+    """Test check_line with an environment variable"""
+    errors, warnings = checker.check_line("MAILTO=test@example.com", 1, "test.txt")
+    assert errors == []
+    assert warnings == []
+
+
 # ============================================================================
 # Tests for special file types (char device, block device, socket, fifo)
 # ============================================================================
diff --git a/tests/test_logger.py b/tests/test_logger.py
new file mode 100644
index 0000000..bc700aa
--- /dev/null
+++ b/tests/test_logger.py
@@ -0,0 +1,100 @@
+#!/usr/bin/env python3
+
+import logging
+import platform
+import sys
+from unittest.mock import MagicMock, patch
+
+import pytest
+from checkcrontab.logger import ColoredFormatter, setup_logging
+
+# Mock the getwindowsversion function if it doesn't exist (i.e., on non-Windows platforms)
+if not hasattr(sys, "getwindowsversion"):
+
+    class MockWindowsVersion:
+        def __init__(self, major, build):
+            self.major = major
+            self.build = build
+
+    sys.getwindowsversion = MagicMock(return_value=MockWindowsVersion(10, 10586))
+
+
+class TestColoredFormatter:
+    @pytest.fixture
+    def log_record(self):
+        return logging.LogRecord(
+            "test", logging.INFO, "/test", 1, "test message", None, None
+        )
+
+    def test_formatter_no_color(self, log_record):
+        formatter = ColoredFormatter(fmt="%(message)s", use_colors=False)
+        formatted_message = formatter.format(log_record)
+        assert formatted_message == "test message"
+        assert "\033" not in formatted_message
+
+    def test_formatter_with_color(self, log_record):
+        formatter = ColoredFormatter(fmt="%(levelname)s: %(message)s", use_colors=True)
+        with patch("platform.system", return_value="Linux"):
+            formatted_message = formatter.format(log_record)
+            assert "test message" in formatted_message
+            assert "\033[0;32mINFO\033[0m" in formatted_message
+
+    @patch("platform.system", return_value="Windows")
+    def test_windows_color_compatibility_supported(self, mock_system, log_record):
+        with patch(
+            "sys.getwindowsversion",
+            return_value=MagicMock(major=10, build=10586),
+        ):
+            formatter = ColoredFormatter(
+                fmt="%(levelname)s: %(message)s", use_colors=True
+            )
+            assert formatter._get_color_compatibility() is True
+            formatted_message = formatter.format(log_record)
+            assert "\033[0;32mINFO\033[0m" in formatted_message
+
+    @patch("platform.system", return_value="Windows")
+    def test_windows_color_compatibility_not_supported(self, mock_system, log_record):
+        with patch(
+            "sys.getwindowsversion",
+            return_value=MagicMock(major=10, build=10000),
+        ):
+            formatter = ColoredFormatter(fmt="%(message)s", use_colors=True)
+            assert formatter._get_color_compatibility() is False
+            formatted_message = formatter.format(log_record)
+            assert "\033" not in formatted_message
+
+    @patch("platform.system", return_value="Windows")
+    def test_windows_color_compatibility_exception(self, mock_system, log_record):
+        with patch("sys.getwindowsversion", side_effect=Exception()):
+            formatter = ColoredFormatter(fmt="%(message)s", use_colors=True)
+            assert formatter._get_color_compatibility() is False
+            formatted_message = formatter.format(log_record)
+            assert "\033" not in formatted_message
+
+
+class TestSetupLogging:
+    @patch("logging.basicConfig")
+    def test_setup_logging_debug(self, mock_basic_config):
+        setup_logging(debug=True)
+        mock_basic_config.assert_called_once()
+        assert mock_basic_config.call_args[1]["level"] == logging.DEBUG
+
+    @patch("logging.basicConfig")
+    def test_setup_logging_info(self, mock_basic_config):
+        setup_logging(debug=False)
+        mock_basic_config.assert_called_once()
+        assert mock_basic_config.call_args[1]["level"] == logging.INFO
+
+    @patch("logging.StreamHandler", MagicMock())
+    @patch("logging.basicConfig")
+    def test_setup_logging_stderr(self, mock_basic_config):
+        with patch("sys.stderr") as mock_stderr:
+            setup_logging(use_stderr=True)
+            logging.StreamHandler.assert_called_with(mock_stderr)
+
+    @patch("logging.StreamHandler", MagicMock())
+    @patch("logging.basicConfig")
+    def test_setup_logging_stdout(self, mock_basic_config):
+        with patch("sys.stdout") as mock_stdout:
+            setup_logging(use_stderr=False)
+            logging.StreamHandler.assert_called_with(mock_stdout)