diff --git a/gitignore_generator/tests/test_validator.py b/gitignore_generator/tests/test_validator.py
new file mode 100644
index 0000000..f43c981
--- /dev/null
+++ b/gitignore_generator/tests/test_validator.py
@@ -0,0 +1,107 @@
+"""Tests for validator."""
+
+import pytest
+
+from gitignore_generator.validator import Validator, ValidationIssue
+
+
+class TestValidator:
+    """Tests for Validator class."""
+
+    @pytest.fixture
+    def validator(self):
+        """Create validator instance."""
+        return Validator()
+
+    def test_valid_content(self, validator):
+        """Test validation of valid content."""
+        content = "__pycache__/\n*.pyc\nnode_modules/\n"
+        summary = validator.get_summary(content)
+        assert summary["valid"] is True
+        assert summary["errors"] == 0
+
+    def test_trailing_slash_warning(self, validator):
+        """Test detection of trailing slashes."""
+        content = "dir/\n"
+        summary = validator.get_summary(content)
+        assert summary["warnings"] >= 1
+        has_trailing = any(
+            "trailing_slash" in issue.issue_type
+            for issue in summary["issues"]
+        )
+        assert has_trailing
+
+    def test_duplicate_pattern_warning(self, validator):
+        """Test detection of duplicate patterns."""
+        content = "__pycache__\n__pycache__\n"
+        summary = validator.get_summary(content)
+        assert summary["warnings"] >= 1
+
+    def test_backslash_escape_error(self, validator):
+        """Test detection of invalid backslash escapes."""
+        content = "test\\nfile\n"
+        summary = validator.get_summary(content)
+        assert summary["errors"] >= 1
+
+    def test_double_star_warning(self, validator):
+        """Test detection of problematic double star usage."""
+        content = "test**/file\n"
+        summary = validator.get_summary(content)
+        assert summary["warnings"] >= 1
+
+    def test_double_negation_warning(self, validator):
+        """Test detection of consecutive negations."""
+        content = "!file.txt\n!other.txt\n"
+        summary = validator.get_summary(content)
+        assert summary["warnings"] >= 1
+
+    def test_validate_pattern_valid(self, validator):
+        """Test validating a single valid pattern."""
+        issue = validator.validate_pattern("*.pyc")
+        assert issue is None
+
+    def test_validate_pattern_invalid(self, validator):
+        """Test validating an invalid pattern."""
+        issue = validator.validate_pattern("test\\n")
+        assert issue is not None
+        assert issue.severity == "error"
+
+    def test_comments_ignored(self, validator):
+        """Test that comments are ignored."""
+        content = "# This is a comment\n__pycache__/\n"
+        summary = validator.get_summary(content)
+        assert summary["valid"] is True
+
+    def test_empty_lines_ignored(self, validator):
+        """Test that empty lines are ignored."""
+        content = "\n\n\n__pycache__/\n\n"
+        summary = validator.get_summary(content)
+        assert summary["valid"] is True
+
+    def test_is_valid_method(self, validator):
+        """Test is_valid method."""
+        assert validator.is_valid("*.pyc") is True
+        assert validator.is_valid("test\\n") is False
+
+    def test_validation_issue_line_number(self, validator):
+        """Test that line numbers are correct in issues."""
+        content = "valid_line.pyc\ntest\\n\n"
+        summary = validator.get_summary(content)
+        backslash_issue = next(
+            (i for i in summary["issues"] if i.issue_type == "invalid_escape"),
+            None
+        )
+        assert backslash_issue is not None
+        assert backslash_issue.line_number == 2
+
+    def test_empty_content_valid(self, validator):
+        """Test that empty content is valid."""
+        summary = validator.get_summary("")
+        assert summary["valid"] is True
+        assert summary["errors"] == 0
+
+    def test_only_comments_valid(self, validator):
+        """Test that only comments is valid."""
+        content = "# Comment 1\n# Comment 2\n"
+        summary = validator.get_summary(content)
+        assert summary["valid"] is True