diff --git a/app/tests/test_testing.py b/app/tests/test_testing.py
new file mode 100644
index 0000000..edf29d0
--- /dev/null
+++ b/app/tests/test_testing.py
@@ -0,0 +1,239 @@
+from promptforge.testing.validator import (
+    RegexValidator,
+    JSONSchemaValidator,
+    LengthValidator,
+    ContainsValidator,
+    CompositeValidator,
+)
+from promptforge.testing.metrics import MetricsCollector, MetricsSample
+from promptforge.testing.results import TestSessionResults, ResultFormatter
+from promptforge.testing.ab_test import ABTestConfig
+
+
+class TestRegexValidator:
+    """Tests for RegexValidator."""
+
+    def test_valid_pattern(self):
+        """Test matching pattern."""
+        validator = RegexValidator(r"^Hello.*")
+        is_valid, error = validator.validate("Hello, World!")
+        assert is_valid is True
+        assert error is None
+
+    def test_invalid_pattern(self):
+        """Test non-matching pattern."""
+        validator = RegexValidator(r"^Hello.*")
+        is_valid, error = validator.validate("Goodbye")
+        assert is_valid is False
+        assert error is not None
+
+    def test_case_insensitive(self):
+        """Test case insensitive matching."""
+        validator = RegexValidator(r"hello", flags=2)  # re.IGNORECASE
+        is_valid, _ = validator.validate("HELLO")
+        assert is_valid is True
+
+
+class TestJSONSchemaValidator:
+    """Tests for JSONSchemaValidator."""
+
+    def test_valid_json(self):
+        """Test valid JSON against schema."""
+        schema = {
+            "type": "object",
+            "properties": {
+                "name": {"type": "string"},
+                "age": {"type": "number"}
+            }
+        }
+        validator = JSONSchemaValidator(schema)
+        is_valid, error = validator.validate('{"name": "Alice", "age": 30}')
+        assert is_valid is True
+
+    def test_invalid_json(self):
+        """Test invalid JSON."""
+        validator = JSONSchemaValidator({})
+        is_valid, error = validator.validate("not json")
+        assert is_valid is False
+        assert "JSON" in error
+
+    def test_type_mismatch(self):
+        """Test type mismatch in schema."""
+        schema = {
+            "type": "object",
+            "properties": {
+                "count": {"type": "integer"}
+            }
+        }
+        validator = JSONSchemaValidator(schema)
+        is_valid, error = validator.validate('{"count": "not a number"}')
+        assert is_valid is False
+
+
+class TestLengthValidator:
+    """Tests for LengthValidator."""
+
+    def test_within_bounds(self):
+        """Test valid length."""
+        validator = LengthValidator(min_length=5, max_length=100)
+        is_valid, error = validator.validate("Hello, World!")
+        assert is_valid is True
+
+    def test_too_short(self):
+        """Test string too short."""
+        validator = LengthValidator(min_length=10)
+        is_valid, error = validator.validate("Hi")
+        assert is_valid is False
+        assert "short" in error
+
+    def test_too_long(self):
+        """Test string too long."""
+        validator = LengthValidator(max_length=5)
+        is_valid, error = validator.validate("Hello, World!")
+        assert is_valid is False
+        assert "long" in error
+
+
+class TestContainsValidator:
+    """Tests for ContainsValidator."""
+
+    def test_contains_string(self):
+        """Test string contains required content."""
+        validator = ContainsValidator(required_strings=["hello", "world"])
+        is_valid, error = validator.validate("Say hello to the world")
+        assert is_valid is True
+
+    def test_missing_content(self):
+        """Test missing required content."""
+        validator = ContainsValidator(required_strings=["hello", "world"])
+        is_valid, error = validator.validate("Just some random text")
+        assert is_valid is False
+
+
+class TestCompositeValidator:
+    """Tests for CompositeValidator."""
+
+    def test_all_mode(self):
+        """Test AND mode validation."""
+        validators = [
+            RegexValidator(r"^Hello.*"),
+            LengthValidator(min_length=5),
+        ]
+        composite = CompositeValidator(validators, mode="all")
+        is_valid, _ = composite.validate("Hello, World!")
+        assert is_valid is True
+
+    def test_any_mode(self):
+        """Test OR mode validation."""
+        validators = [
+            RegexValidator(r"^Hello.*"),
+            RegexValidator(r"^Goodbye.*"),
+        ]
+        composite = CompositeValidator(validators, mode="any")
+        is_valid, _ = composite.validate("Goodbye, World!")
+        assert is_valid is True
+
+
+class TestMetricsCollector:
+    """Tests for MetricsCollector."""
+
+    def test_record_sample(self):
+        """Test recording metrics sample."""
+        collector = MetricsCollector()
+        sample = MetricsSample(
+            latency_ms=100.0,
+            tokens_total=50,
+            validation_passed=True,
+        )
+        collector.record(sample)
+
+        summary = collector.get_summary()
+        assert summary.count == 1
+        assert summary.latency["avg"] == 100.0
+
+    def test_record_from_response(self):
+        """Test recording from provider response."""
+        collector = MetricsCollector()
+        sample = collector.record_from_response(
+            latency_ms=50.0,
+            usage={"prompt_tokens": 10, "completion_tokens": 5},
+            validation_passed=True,
+        )
+        assert sample.tokens_total == 15
+
+    def test_clear_samples(self):
+        """Test clearing samples."""
+        collector = MetricsCollector()
+        collector.record(MetricsSample())
+        collector.clear()
+
+        summary = collector.get_summary()
+        assert summary.count == 0
+
+    def test_compare_collectors(self):
+        """Test comparing two collectors."""
+        collector1 = MetricsCollector()
+        collector1.record(MetricsSample(latency_ms=100.0))
+
+        collector2 = MetricsCollector()
+        collector2.record(MetricsSample(latency_ms=200.0))
+
+        comparison = collector1.compare(collector2)
+        assert comparison["latency_delta_ms"] == 100.0
+
+
+class TestResultFormatter:
+    """Tests for ResultFormatter."""
+
+    def test_format_text(self):
+        """Test formatting results as text."""
+        from promptforge.testing.results import TestResult
+        results = TestSessionResults(
+            test_id="test-123",
+            name="My Test",
+        )
+        results.results.append(TestResult(
+            test_id="1",
+            prompt_name="prompt1",
+            provider="openai",
+            success=True,
+            response="Hello",
+        ))
+
+        formatted = ResultFormatter.format_text(results)
+        assert "My Test" in formatted
+        assert "PASS" in formatted
+
+    def test_format_json(self):
+        """Test formatting results as JSON."""
+        results = TestSessionResults(
+            test_id="test-123",
+            name="My Test",
+        )
+
+        formatted = ResultFormatter.format_json(results)
+        import json
+        data = json.loads(formatted)
+        assert data["name"] == "My Test"
+        assert "results" in data
+
+
+class TestABTestConfig:
+    """Tests for ABTestConfig."""
+
+    def test_default_config(self):
+        """Test default A/B test configuration."""
+        config = ABTestConfig()
+        assert config.iterations == 3
+        assert config.parallel is False
+        assert config.temperature == 0.7
+
+    def test_custom_config(self):
+        """Test custom A/B test configuration."""
+        config = ABTestConfig(
+            iterations=5,
+            parallel=True,
+            temperature=0.5,
+        )
+        assert config.iterations == 5
+        assert config.parallel is True