diff --git a/tests/test_registry_and_integration.py b/tests/test_registry_and_integration.py
new file mode 100644
index 0000000..e19fc42
--- /dev/null
+++ b/tests/test_registry_and_integration.py
@@ -0,0 +1,387 @@
+# tests/test_registry_and_integration.py
+"""
+Comprehensive tests for Issue #13: Add more tests.
+
+Tests cover:
+- Registry functionality (personalities as objects and strings)
+- Adding to the registry
+- Specific personality behaviors
+- message_every smoothing and averages
+"""
+
+import pytest
+import torch
+
+from emotigrad import EmotionalOptimizer
+from emotigrad.personalities import (
+    QuietPersonality,
+    get_personality,
+    list_personalities,
+    register_personality,
+    sassy,
+    wholesome,
+)
+
+
+class TestRegistryWithStrings:
+    """Test that personalities can be provided as registry strings."""
+
+    def test_optimizer_accepts_string_personality(self):
+        """EmotionalOptimizer should accept a string personality name."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        emo_opt = EmotionalOptimizer(optimizer, personality="wholesome")
+
+        # Should resolve the string to the actual personality
+        assert callable(emo_opt.personality)
+
+    def test_optimizer_resolves_all_registered_personalities(self):
+        """All registered personality strings should be resolvable."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        for name in list_personalities():
+            emo_opt = EmotionalOptimizer(optimizer, personality=name)
+            assert callable(emo_opt.personality)
+
+    def test_optimizer_raises_on_unknown_personality_string(self):
+        """Unknown personality string should raise KeyError."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        with pytest.raises(KeyError):
+            EmotionalOptimizer(optimizer, personality="nonexistent_personality")
+
+
+class TestRegistryWithObjects:
+    """Test that personalities can be provided as callable objects."""
+
+    def test_optimizer_accepts_function_personality(self):
+        """EmotionalOptimizer should accept a function as personality."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        def custom_personality(loss, prev_loss, step):
+            return "Custom message"
+
+        emo_opt = EmotionalOptimizer(optimizer, personality=custom_personality)
+
+        assert emo_opt.personality == custom_personality
+
+    def test_optimizer_accepts_class_instance_personality(self):
+        """EmotionalOptimizer should accept a class instance as personality."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        quiet = QuietPersonality(every_n_steps=5)
+        emo_opt = EmotionalOptimizer(optimizer, personality=quiet)
+
+        assert emo_opt.personality == quiet
+
+    def test_optimizer_accepts_lambda_personality(self):
+        """EmotionalOptimizer should accept a lambda as personality."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        emo_opt = EmotionalOptimizer(
+            optimizer, personality=lambda l, p, s: f"Lambda: {l}"
+        )
+
+        assert callable(emo_opt.personality)
+
+
+class TestAddingToRegistry:
+    """Test adding custom personalities to the registry."""
+
+    def test_register_new_personality(self):
+        """Should be able to register a new personality."""
+
+        def my_custom_personality(loss, prev_loss, step):
+            return "My custom message"
+
+        # Use a unique name to avoid conflicts
+        name = "test_custom_personality_unique"
+        register_personality(name, my_custom_personality)
+
+        assert name in list_personalities()
+        assert get_personality(name) == my_custom_personality
+
+    def test_register_class_personality(self):
+        """Should be able to register a class-based personality."""
+
+        class MyClassPersonality:
+            def __call__(self, loss, prev_loss, step):
+                return "Class message"
+
+        name = "test_class_personality_unique"
+        instance = MyClassPersonality()
+        register_personality(name, instance)
+
+        assert name in list_personalities()
+        retrieved = get_personality(name)
+        assert callable(retrieved)
+
+    def test_cannot_overwrite_existing_without_flag(self):
+        """Should raise ValueError when overwriting without flag."""
+
+        def dummy(loss, prev_loss, step):
+            return "Dummy"
+
+        # wholesome is already registered
+        with pytest.raises(ValueError):
+            register_personality("wholesome", dummy, overwrite=False)
+
+    def test_can_overwrite_with_flag(self):
+        """Should allow overwriting with overwrite=True."""
+        original = get_personality("sassy")
+
+        def new_sassy(loss, prev_loss, step):
+            return "New sassy"
+
+        register_personality("sassy", new_sassy, overwrite=True)
+
+        assert get_personality("sassy") == new_sassy
+
+        # Restore original
+        register_personality("sassy", original, overwrite=True)
+
+
+class TestSpecificPersonalities:
+    """Test specific personality behaviors."""
+
+    def test_wholesome_first_step(self):
+        """Wholesome should return encouraging message on first step."""
+        result = wholesome(loss=1.0, prev_loss=None, step=1)
+        assert "✨" in result or "Let's" in result.lower()
+        assert "1.0" in result
+
+    def test_wholesome_loss_decrease(self):
+        """Wholesome should celebrate loss decrease."""
+        result = wholesome(loss=0.5, prev_loss=1.0, step=2)
+        assert "💖" in result or "Nice" in result
+
+    def test_wholesome_loss_increase(self):
+        """Wholesome should be encouraging on loss increase."""
+        result = wholesome(loss=1.5, prev_loss=1.0, step=2)
+        assert "🌱" in result or "okay" in result.lower()
+
+    def test_sassy_first_step(self):
+        """Sassy should be dismissive on first step."""
+        result = sassy(loss=1.0, prev_loss=None, step=1)
+        assert "😒" in result or "Fine" in result
+
+    def test_sassy_loss_decrease(self):
+        """Sassy should be grudgingly approving on loss decrease."""
+        result = sassy(loss=0.5, prev_loss=1.0, step=2)
+        assert "👏" in result or "About time" in result
+
+    def test_sassy_loss_increase(self):
+        """Sassy should be sarcastic on loss increase."""
+        result = sassy(loss=1.5, prev_loss=1.0, step=2)
+        assert "🙄" in result or "Bold" in result.lower()
+
+    def test_quiet_personality_respects_interval(self):
+        """QuietPersonality should only output at specified intervals."""
+        quiet = QuietPersonality(every_n_steps=5)
+
+        # Steps 1-4 should return None
+        for step in range(1, 5):
+            assert quiet(loss=1.0, prev_loss=None, step=step) is None
+
+        # Step 5 should return a message
+        result = quiet(loss=1.0, prev_loss=None, step=5)
+        assert result is not None
+        assert "Step 5" in result
+
+
+class TestMessageEverySmoothing:
+    """Test message_every parameter and loss averaging."""
+
+    def test_message_every_counts_steps_correctly(self):
+        """Should emit messages at correct intervals."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+
+        def capture(msg):
+            messages.append(msg)
+
+        def echo(loss, prev, step):
+            return f"step={step}"
+
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality=echo,
+            print_fn=capture,
+            message_every=2,
+        )
+
+        # Run 6 steps
+        for _ in range(6):
+            emo_opt.step(loss=1.0)
+
+        # Should have messages at steps 2, 4, 6
+        assert len(messages) == 3
+
+    def test_message_every_averages_losses(self):
+        """Loss should be averaged over the message_every window."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        captured_losses = []
+
+        def capture_loss(loss, prev, step):
+            captured_losses.append(loss)
+            return "msg"
+
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality=capture_loss,
+            print_fn=lambda x: None,
+            message_every=3,
+        )
+
+        # Provide losses: 1, 2, 3 -> avg = 2
+        for loss in [1.0, 2.0, 3.0]:
+            emo_opt.step(loss=loss)
+
+        assert len(captured_losses) == 1
+        assert abs(captured_losses[0] - 2.0) < 0.01
+
+    def test_message_every_tracks_previous_average(self):
+        """Previous loss should be the previous window's average."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        prev_losses = []
+
+        def capture_prev(loss, prev, step):
+            prev_losses.append(prev)
+            return "msg"
+
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality=capture_prev,
+            print_fn=lambda x: None,
+            message_every=2,
+        )
+
+        # Window 1: [1, 3] avg=2
+        # Window 2: [5, 7] avg=6
+        for loss in [1.0, 3.0, 5.0, 7.0]:
+            emo_opt.step(loss=loss)
+
+        # First window: prev is None
+        assert prev_losses[0] is None
+        # Second window: prev is 2.0
+        assert abs(prev_losses[1] - 2.0) < 0.01
+
+    def test_message_every_zero_disables_messages(self):
+        """message_every=0 should disable all messages."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality=lambda l, p, s: "msg",
+            print_fn=messages.append,
+            message_every=0,
+        )
+
+        for _ in range(10):
+            emo_opt.step(loss=1.0)
+
+        assert len(messages) == 0
+
+    def test_message_every_one_emits_every_step(self):
+        """message_every=1 should emit a message every step."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality=lambda l, p, s: "msg",
+            print_fn=messages.append,
+            message_every=1,
+        )
+
+        for _ in range(5):
+            emo_opt.step(loss=1.0)
+
+        assert len(messages) == 5
+
+
+class TestIntegrationScenarios:
+    """Integration tests for realistic usage scenarios."""
+
+    def test_full_training_loop_with_string_personality(self):
+        """Test a complete training loop with string personality."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality="wholesome",
+            print_fn=messages.append,
+            message_every=1,
+        )
+
+        x = torch.randn(4, 2)
+        y = torch.randn(4, 1)
+
+        for _ in range(3):
+            emo_opt.zero_grad()
+            pred = model(x)
+            loss = (pred - y).pow(2).mean()
+            loss.backward()
+            emo_opt.step(loss=loss.item())
+
+        assert len(messages) == 3
+        assert emo_opt.step_count == 3
+
+    def test_switching_personalities_mid_training(self):
+        """Test changing personality during training."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality="wholesome",
+            print_fn=messages.append,
+        )
+
+        # Train with wholesome
+        emo_opt.step(loss=1.0)
+
+        # Switch to sassy
+        emo_opt.personality = get_personality("sassy")
+        emo_opt.step(loss=0.5)
+
+        # Should have different message styles
+        assert len(messages) == 2
+
+    def test_disabled_optimizer_produces_no_messages(self):
+        """Disabled optimizer should not produce any messages."""
+        model = torch.nn.Linear(2, 1)
+        optimizer = torch.optim.SGD(model.parameters(), lr=0.1)
+
+        messages = []
+        emo_opt = EmotionalOptimizer(
+            optimizer,
+            personality="wholesome",
+            print_fn=messages.append,
+            enabled=False,
+        )
+
+        for _ in range(10):
+            emo_opt.step(loss=1.0)
+
+        assert len(messages) == 0