diff --git a/tests/test_formatters.py b/tests/test_formatters.py
new file mode 100644
index 0000000..b365f1b
--- /dev/null
+++ b/tests/test_formatters.py
@@ -0,0 +1,80 @@
+"""Tests for the formatter module."""
+
+import json
+import pytest
+
+from configconverter.formatters import Formatter
+from configconverter.exceptions import IndentationError
+
+
+class TestFormatter:
+    """Tests for the Formatter class."""
+
+    @pytest.fixture
+    def formatter(self):
+        return Formatter()
+
+    def test_format_json_with_indent_2(self, formatter):
+        content = '{"name":"test","value":123}'
+        result = formatter.format(content, indent=2, format="json")
+        assert "\n  " in result
+
+    def test_format_json_with_indent_4(self, formatter):
+        content = '{"name":"test","value":123}'
+        result = formatter.format(content, indent=4, format="json")
+        assert "\n    " in result
+
+    def test_format_json_compact(self, formatter):
+        content = '{"name":"test","value":123}'
+        result = formatter.format(content, indent=2, compact=True, format="json")
+        assert result.strip() == '{"name":"test","value":123}'
+
+    def test_format_invalid_indent(self, formatter):
+        content = '{"name":"test"}'
+        with pytest.raises(IndentationError):
+            formatter.format(content, indent=3, format="json")
+
+    def test_format_json_to_yaml(self, formatter):
+        content = '{"name": "test", "value": 123}'
+        result = formatter.format(content, format="yaml")
+        assert "name: test" in result
+
+    def test_format_yaml_to_json(self, formatter):
+        content = 'name: test\nvalue: 123\n'
+        result = formatter.format(content, format="json")
+        data = json.loads(result)
+        assert data["name"] == "test"
+        assert data["value"] == 123
+
+    def test_format_toml_to_json(self, formatter):
+        content = 'name = "test"\nvalue = 123\n'
+        result = formatter.format(content, format="json")
+        data = json.loads(result)
+        assert data["name"] == "test"
+        assert data["value"] == 123
+
+    def test_to_json_method(self, formatter):
+        content = 'name: test\n'
+        result = formatter.to_json(content, indent=4)
+        data = json.loads(result)
+        assert data["name"] == "test"
+
+    def test_to_yaml_method(self, formatter):
+        content = '{"name": "test"}'
+        result = formatter.to_yaml(content)
+        assert "name: test" in result
+
+    def test_to_toml_method(self, formatter):
+        content = '{"name": "test"}'
+        result = formatter.to_toml(content)
+        assert 'name = "test"' in result
+
+    def test_nested_structure_formatting(self, formatter):
+        content = '{"a":{"b":{"c":"d"}}}'
+        result = formatter.format(content, indent=2, format="json")
+        assert '"c": "d"' in result
+
+    def test_array_formatting(self, formatter):
+        content = '[1,2,3,4,5]'
+        result = formatter.format(content, indent=2, format="json")
+        assert "[\n  1," in result