diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..6e112d6
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,29 @@
+name: CI
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+jobs:
+  compile:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: arduino/compile-sketches@v1
+        with:
+          sketch-paths: |
+            - .
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Install test dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install pytest
+      - name: Run logic tests
+        run: |
+          if [ -d tests ]; then python -m pytest tests/ -v; fi
diff --git a/.gitignore b/.gitignore
index 496ee2c..4785022 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,14 @@
-.DS_Store
\ No newline at end of file
+.DS_Store
+# Auto-added by Marisol pipeline
+node_modules/
+__pycache__/
+*.pyc
+.pytest_cache/
+*.o
+*.so
+.env
+debug_*.py
+.cache/
+dist/
+build/
+*.egg-info/
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..53aba3b
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,45 @@
+"""Auto-generated conftest.py -- stubs for Arduino/embedded C testing.
+
+Strategy: Arduino .ino/.cpp files can't be imported in Python, so we test by
+re-implementing the core algorithms (state machines, math, protocol encoding,
+parsers) in Python and verifying them with pytest. The conftest provides mock
+serial and common helper dependencies.
+"""
+import sys
+import os
+import pytest
+from unittest.mock import MagicMock, patch
+
+# Add repo root to path so test files can import source modules
+sys.path.insert(0, '')
+
+# Mock common Arduino Python helper dependencies
+for mod_name in ['serial', 'serial.tools', 'serial.tools.list_ports',
+                 'pyserial', 'pyfirmata', 'pyfirmata2']:
+    sys.modules[mod_name] = MagicMock()
+
+
+class ArduinoConstants:
+    """Provides Arduino-style constants for Python re-implementations."""
+    HIGH = 1
+    LOW = 0
+    INPUT = 0
+    OUTPUT = 1
+    INPUT_PULLUP = 2
+    A0, A1, A2, A3, A4, A5 = range(14, 20)
+
+    @staticmethod
+    def map_value(x, in_min, in_max, out_min, out_max):
+        """Arduino map() function."""
+        return int((x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min)
+
+    @staticmethod
+    def constrain(x, a, b):
+        """Arduino constrain() function."""
+        return max(a, min(x, b))
+
+
+@pytest.fixture
+def arduino():
+    """Provides Arduino-like constants and helpers for testing re-implemented logic."""
+    return ArduinoConstants()
diff --git a/tests/test_inplants.py b/tests/test_inplants.py
new file mode 100644
index 0000000..cdaf05a
--- /dev/null
+++ b/tests/test_inplants.py
@@ -0,0 +1,173 @@
+"""Tests for in-plants Arduino project.
+
+Tests re-implemented algorithms from inplants-argon.ino and inplants-xenon.ino
+"""
+
+import pytest
+
+
+def map_value(x, in_min, in_max, out_min, out_max):
+    """Re-implementation of Arduino's map() function."""
+    return int((x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min)
+
+
+def constrain(x, low, high):
+    """Re-implementation of Arduino's constrain() function."""
+    return max(low, min(x, high))
+
+
+def analog_to_percentage(analog_value):
+    """Convert analog reading (0-4095) to moisture percentage.
+    
+    From inplants-argon.ino and inplants-xenon.ino:
+    float moisture_percentage = (100 - ( (moisture_analog/4095.00) * 100 ) );
+    """
+    return 100 - ((analog_value / 4095.00) * 100)
+
+
+def analog_to_voltage(analog_value):
+    """Convert battery analog reading to voltage.
+    
+    From inplants-xenon.ino:
+    float voltage = analogRead(BATT) * 0.0011224;
+    """
+    return analog_value * 0.0011224
+
+
+class TestMoisturePercentage:
+    """Test the moisture percentage calculation."""
+    
+    def test_dry_sensor(self):
+        """Dry sensor should read ~0% moisture (high analog value)."""
+        # When sensor is dry, analog reading is high (near 4095)
+        analog_dry = 4095
+        percentage = analog_to_percentage(analog_dry)
+        assert percentage == 0.0
+    
+    def test_wet_sensor(self):
+        """Wet sensor should read ~100% moisture (low analog value)."""
+        # When sensor is wet, analog reading is low (near 0)
+        analog_wet = 0
+        percentage = analog_to_percentage(analog_wet)
+        assert percentage == 100.0
+    
+    def test_mid_moisture(self):
+        """Mid-range moisture level."""
+        # Mid-range analog value
+        analog_mid = 2048
+        percentage = analog_to_percentage(analog_mid)
+        # Should be approximately 50%
+        assert 49.9 <= percentage <= 50.1
+    
+    def test_realistic_dry_reading(self):
+        """Test with a realistic dry sensor reading."""
+        # Realistic dry reading around 3500-4000
+        analog_value = 3800
+        percentage = analog_to_percentage(analog_value)
+        # Should be around 7-8% moisture
+        assert 7.0 <= percentage <= 8.0
+    
+    def test_realistic_wet_reading(self):
+        """Test with a realistic wet sensor reading."""
+        # Realistic wet reading around 1000-1500
+        analog_value = 1200
+        percentage = analog_to_percentage(analog_value)
+        # Should be around 70-75% moisture
+        assert 70.0 <= percentage <= 75.0
+
+
+class TestBatteryVoltage:
+    """Test the battery voltage calculation."""
+    
+    def test_zero_voltage(self):
+        """Zero analog reading should give zero voltage."""
+        assert analog_to_voltage(0) == 0.0
+    
+    def test_full_voltage(self):
+        """Test with a typical battery voltage.
+        
+        A fully charged LiPo battery is around 4.2V.
+        4.2 / 0.0011224 ≈ 3742 analog units
+        """
+        analog_value = 3742
+        voltage = analog_to_voltage(analog_value)
+        assert 4.19 <= voltage <= 4.21
+    
+    def test_mid_voltage(self):
+        """Test with mid battery voltage (3.7V typical)."""
+        analog_value = 3297  # 3.7 / 0.0011224
+        voltage = analog_to_voltage(analog_value)
+        assert 3.69 <= voltage <= 3.71
+    
+    def test_low_voltage(self):
+        """Test with low battery voltage (3.0V cutoff)."""
+        analog_value = 2673  # 3.0 / 0.0011224
+        voltage = analog_to_voltage(analog_value)
+        assert 2.99 <= voltage <= 3.01
+
+
+class TestConstrain:
+    """Test the constrain function."""
+    
+    def test_within_bounds(self):
+        """Value within bounds should be unchanged."""
+        assert constrain(50, 0, 100) == 50
+    
+    def test_below_bounds(self):
+        """Value below bounds should be constrained to low."""
+        assert constrain(-10, 0, 100) == 0
+    
+    def test_above_bounds(self):
+        """Value above bounds should be constrained to high."""
+        assert constrain(150, 0, 100) == 100
+
+
+class TestMapFunction:
+    """Test the map function re-implementation."""
+    
+    def test_map_mid_range(self):
+        """Map mid-range value."""
+        assert map_value(512, 0, 1023, 0, 255) == 127
+    
+    def test_map_full_range(self):
+        """Map full range value."""
+        assert map_value(1023, 0, 1023, 0, 255) == 255
+    
+    def test_map_zero(self):
+        """Map zero value."""
+        assert map_value(0, 0, 1023, 0, 255) == 0
+
+
+class TestLEDSequence:
+    """Test the LED blinking sequence logic."""
+    
+    def test_led_blink_duration(self):
+        """Verify LED blink timing (200ms on, 200ms off, 3x)."""
+        # From setup(): 3 blinks with 200ms on/off each
+        # Total duration = 3 * (200 + 200) = 1200ms
+        blink_duration = 200
+        num_blinks = 3
+        total_duration = num_blinks * blink_duration * 2
+        assert total_duration == 1200
+
+
+class TestTimingIntervals:
+    """Test the timing intervals from the main loop."""
+    
+    def test_argon_interval(self):
+        """Argon publishes every 30 minutes (1800000ms)."""
+        # From inplants-argon.ino: delay(1800000)
+        interval_ms = 1800000
+        assert interval_ms == 30 * 60 * 1000  # 30 minutes
+    
+    def test_xenon_charging_interval(self):
+        """Xenon on USB publishes every 10 minutes (600000ms)."""
+        # From inplants-xenon.ino else branch: delay(600000)
+        interval_ms = 600000
+        assert interval_ms == 10 * 60 * 1000  # 10 minutes
+    
+    def test_xenon_sleep_interval(self):
+        """Xenon on battery sleeps for 12 hours (43200 seconds)."""
+        # From inplants-xenon.ino: System.sleep(D1,RISING,43200)
+        sleep_seconds = 43200
+        assert sleep_seconds == 12 * 60 * 60  # 12 hours