diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_formatter.py b/tests/test_formatter.py
new file mode 100644
index 0000000..567061a
--- /dev/null
+++ b/tests/test_formatter.py
@@ -0,0 +1,81 @@
+import json
+import logging
+from pathlib import Path
+from unittest import TestCase
+from unittest.mock import patch
+
+from bunyan_formatter import BunyanFormatter
+
+
+class TestBunyanFormatter(TestCase):
+    def setUp(self):
+        self.project_name = "test_project"
+        self.project_root = Path("/path/to/project")
+        self.formatter = BunyanFormatter(self.project_name, self.project_root)
+
+    def create_log_record(self, level, msg, pathname):
+        return logging.LogRecord(
+            name="test_logger", level=level, pathname=pathname, lineno=42, msg=msg, args=(), exc_info=None
+        )
+
+    @patch("socket.gethostname")
+    def test_format_basic(self, mock_gethostname):
+        mock_gethostname.return_value = "test_host"
+        record = self.create_log_record(logging.INFO, "Test message", "/path/to/project/test.py")
+
+        formatted = self.formatter.format(record)
+        log_entry = json.loads(formatted)
+
+        assert log_entry["v"] == 0
+        assert log_entry["name"] == self.project_name
+        assert log_entry["msg"] == "Test message"
+        assert log_entry["level"] == 30
+        assert log_entry["levelname"] == "INFO"
+        assert log_entry["hostname"] == "test_host"
+        assert log_entry["target"] == "test_logger"
+        assert log_entry["line"] == 42
+        assert log_entry["file"] == "test.py"
+
+    def test_format_different_levels(self):
+        levels = [logging.DEBUG, logging.INFO, logging.WARNING, logging.ERROR, logging.CRITICAL]
+        expected_levels = [20, 30, 40, 50, 60]
+
+        for level, expected in zip(levels, expected_levels):
+            record = self.create_log_record(level, f"Test {logging.getLevelName(level)}", "/path/to/project/test.py")
+            formatted = self.formatter.format(record)
+            log_entry = json.loads(formatted)
+            assert log_entry["level"] == expected
+            assert log_entry["levelname"] == logging.getLevelName(level)
+
+    def test_format_file_outside_project(self):
+        record = self.create_log_record(logging.INFO, "Test message", "/path/outside/project/test.py")
+        formatted = self.formatter.format(record)
+        log_entry = json.loads(formatted)
+        assert log_entry["file"] == "/path/outside/project/test.py"
+
+    @patch("socket.gethostname")
+    def test_format_hostname_consistency(self, mock_gethostname):
+        mock_gethostname.return_value = "test_host"
+        record1 = self.create_log_record(logging.INFO, "Message 1", "/path/to/project/test1.py")
+        record2 = self.create_log_record(logging.INFO, "Message 2", "/path/to/project/test2.py")
+
+        formatted1 = self.formatter.format(record1)
+        formatted2 = self.formatter.format(record2)
+
+        log_entry1 = json.loads(formatted1)
+        log_entry2 = json.loads(formatted2)
+
+        assert log_entry1["hostname"] == log_entry2["hostname"]
+
+    def test_format_time(self):
+        record = self.create_log_record(logging.INFO, "Test message", "/path/to/project/test.py")
+        formatted = self.formatter.format(record)
+        log_entry = json.loads(formatted)
+
+        # Check if the time is in the correct format
+        from datetime import datetime
+
+        try:
+            datetime.strptime(log_entry["time"], "%Y-%m-%dT%H:%M:%S.%fZ")
+        except ValueError:
+            self.fail("Time is not in the correct format")