diff --git a/tests/test_testing.py b/tests/test_testing.py
new file mode 100644
index 0000000..3441ca0
--- /dev/null
+++ b/tests/test_testing.py
@@ -0,0 +1,74 @@
+import pytest
+import sys
+from pathlib import Path
+from unittest.mock import Mock, AsyncMock
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
+
+from promptforge.testing.validator import Validator
+from promptforge.testing.metrics import MetricsCollector, ComparisonResult
+from promptforge.testing.ab_test import ABTest, ABTestConfig
+
+
+class TestValidator:
+    def test_valid_json_response(self):
+        validator = Validator.from_prompt_rules([
+            {"type": "json"}
+        ])
+        assert validator.is_valid('{"key": "value"}')
+
+    def test_invalid_json_response(self):
+        validator = Validator.from_prompt_rules([
+            {"type": "json"}
+        ])
+        assert not validator.is_valid("not json")
+
+    def test_regex_validation(self):
+        validator = Validator.from_prompt_rules([
+            {"type": "regex", "pattern": "^\\d+\\. .+", "message": "Must be numbered list"}
+        ])
+        assert validator.is_valid("1. First item")
+        assert not validator.is_valid("Not numbered")
+
+
+class TestMetricsCollector:
+    def test_compare_metrics(self):
+        from promptforge.testing.metrics import TestMetrics
+
+        collector = MetricsCollector()
+        metrics1 = TestMetrics(
+            test_id="1",
+            prompt_name="Test",
+            provider="openai",
+            model="gpt-4",
+            latency_ms=100.0,
+            success=True,
+            tokens_used=50
+        )
+        metrics2 = TestMetrics(
+            test_id="2",
+            prompt_name="Test",
+            provider="openai",
+            model="gpt-4",
+            latency_ms=200.0,
+            success=True,
+            tokens_used=60
+        )
+
+        result = collector.compare("Test", [metrics1, metrics2])
+        assert result.total_runs == 2
+        assert result.successful_runs == 2
+        assert result.avg_latency_ms == 150.0
+
+
+class TestABTest:
+    def test_config_defaults(self):
+        config = ABTestConfig()
+        assert config.iterations == 3
+        assert config.parallel == False
+
+    def test_ab_test_init(self):
+        mock_provider = Mock()
+        config = ABTestConfig(iterations=5)
+        ab_test = ABTest(mock_provider, config)
+        assert ab_test.config.iterations == 5
\ No newline at end of file