diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..a68bf2b
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,30 @@
+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
+          pip install -r requirements.txt 2>/dev/null || true
+      - name: Run logic tests
+        run: |
+          if [ -d tests ]; then python -m pytest tests/ -v --ignore=tests/test_example.py 2>/dev/null || python -m pytest tests/ -v; fi
\ No newline at end of file
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_example.py b/tests/test_example.py
new file mode 100644
index 0000000..b3d25ea
--- /dev/null
+++ b/tests/test_example.py
@@ -0,0 +1,55 @@
+"""test_example.py — Starter template for Arduino project tests.
+
+Arduino .ino/.cpp files CANNOT be imported in Python. Instead:
+1. READ the source files to understand the algorithms
+2. RE-IMPLEMENT the logic in Python in this test file
+3. Test the Python re-implementation with pytest
+
+The `arduino` fixture provides constants (HIGH, LOW, A0-A5) and helpers
+(map_value, constrain). Also see embedded_mocks.py for I2C/SPI/UART mocks.
+DO NOT modify conftest.py.
+"""
+import pytest
+from embedded_mocks import (
+    MockI2C, MockSPI, MockUART, MockGPIO, MockNeoPixel,
+    MockWiFi, MockBLE, MockPreferences,
+    arduino_map, arduino_constrain, analog_to_voltage,
+)
+
+
+def test_arduino_map():
+    """Test Arduino map() function re-implementation."""
+    assert arduino_map(0, 0, 1023, 0, 255) == 0
+    assert arduino_map(512, 0, 1023, 0, 255) == 127
+    assert arduino_map(1023, 0, 1023, 0, 255) == 255
+
+
+def test_arduino_constrain():
+    """Test Arduino constrain() function."""
+    assert arduino_constrain(150, 0, 100) == 100
+    assert arduino_constrain(-10, 0, 100) == 0
+    assert arduino_constrain(50, 0, 100) == 50
+
+
+def test_analog_voltage_conversion():
+    """Test ADC raw value to voltage conversion."""
+    assert abs(analog_to_voltage(512, bits=10, ref=3.3) - 1.65) < 0.01
+    assert abs(analog_to_voltage(0, bits=10) - 0.0) < 0.01
+    assert abs(analog_to_voltage(1023, bits=10, ref=3.3) - 3.3) < 0.01
+
+
+def test_serial_protocol_example():
+    """Example: test a serial command protocol."""
+    uart = MockUART(baudrate=115200)
+    # Simulate sending a command
+    uart.write(b"AT+CMD\r\n")
+    assert uart._tx_log == b"AT+CMD\r\n"
+    # Simulate receiving a response
+    uart.inject_rx(b"OK\r\n")
+    assert uart.readline() == b"OK\r\n"
+
+
+# TODO: Read the .ino source files and re-implement key algorithms below:
+# def test_state_machine():
+#     """Re-implement the state machine from the Arduino source."""
+#     pass
diff --git a/tests/test_inplants.py b/tests/test_inplants.py
new file mode 100644
index 0000000..1a7ece5
--- /dev/null
+++ b/tests/test_inplants.py
@@ -0,0 +1,158 @@
+"""Tests for in-plants Arduino firmware.
+
+Re-implements key algorithms from inplants-argon.ino and inplants-xenon.ino:
+- Moisture percentage calculation
+- Battery voltage calculation
+- Analog to percentage conversion
+"""
+import pytest
+
+
+def arduino_map(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 arduino_constrain(x, a, b):
+    """Re-implementation of Arduino's constrain() function."""
+    return max(a, min(x, b))
+
+
+def moisture_percentage(moisture_analog):
+    """Re-implementation of moisture percentage calculation from .ino files.
+    
+    Formula: 100 - (moisture_analog / 4095.00) * 100
+    This converts the raw analog reading to a moisture percentage.
+    Higher analog values = more moisture (lower resistance).
+    """
+    return 100 - (moisture_analog / 4095.00) * 100
+
+
+def battery_voltage(analog_value):
+    """Re-implementation of battery voltage calculation.
+    
+    Formula: analog_value * 0.0011224
+    Based on 12-bit ADC (4095 steps) with 3.3V reference.
+    """
+    return analog_value * 0.0011224
+
+
+def test_moisture_percentage_dry_sensor():
+    """Test moisture percentage for dry sensor (high resistance, low analog value)."""
+    # Dry sensor reads ~0-200 analog
+    assert moisture_percentage(0) == 100.0
+    assert moisture_percentage(100) == pytest.approx(97.5555, rel=0.001)
+    assert moisture_percentage(200) == pytest.approx(95.1160, rel=0.001)
+
+
+def test_moisture_percentage_wet_sensor():
+    """Test moisture percentage for wet sensor (low resistance, high analog value)."""
+    # Wet sensor reads ~3500-4000 analog
+    assert moisture_percentage(3500) == pytest.approx(14.5299, rel=0.001)
+    assert moisture_percentage(3800) == pytest.approx(7.2044, rel=0.001)
+    assert moisture_percentage(4000) == pytest.approx(2.3201, rel=0.001)
+
+
+def test_moisture_percentage_mid_range():
+    """Test moisture percentage for mid-range values."""
+    # Mid-range around 2000-2500 analog
+    assert moisture_percentage(2000) == pytest.approx(51.1700, rel=0.001)
+    assert moisture_percentage(2500) == pytest.approx(38.9499, rel=0.001)
+
+
+def test_moisture_percentage_edge_cases():
+    """Test edge cases for moisture calculation."""
+    # Maximum analog value (saturated)
+    assert moisture_percentage(4095) == 0.0
+    # Minimum analog value (completely dry)
+    assert moisture_percentage(0) == 100.0
+
+
+def test_battery_voltage_calculation():
+    """Test battery voltage calculation from ADC reading."""
+    # 0 ADC = 0V
+    assert battery_voltage(0) == 0.0
+    # Mid-range: 1838 * 0.0011224 ≈ 2.06V
+    assert battery_voltage(1838) == pytest.approx(2.0622, rel=0.001)
+    # Full scale: 4095 * 0.0011224 ≈ 4.59V
+    assert battery_voltage(4095) == pytest.approx(4.5970, rel=0.001)
+
+
+def test_battery_voltage_thresholds():
+    """Test battery voltage calculations for common thresholds."""
+    # 3.3V threshold corresponds to ~2940 ADC
+    assert battery_voltage(2940) == pytest.approx(3.2999, rel=0.001)
+    # 3.7V (typical LiPo nominal) corresponds to ~3297 ADC
+    assert battery_voltage(3297) == pytest.approx(3.6985, rel=0.001)
+    # 4.2V (full charge) corresponds to ~3742 ADC
+    assert battery_voltage(3742) == pytest.approx(4.1995, rel=0.001)
+
+
+def test_voltage_to_percentage_conversion():
+    """Test converting battery voltage to percentage using Arduino map."""
+    # Map battery voltage from 3.0V-4.2V to 0-100%
+    # 3.0V = 0%, 4.2V = 100%
+    
+    # 3.0V (2671 ADC) = 0%
+    voltage_3v = battery_voltage(2671)
+    percent_3v = arduino_map(int(voltage_3v * 1000), 3000, 4200, 0, 100)
+    assert percent_3v == 0
+    
+    # 4.2V (3742 ADC) = 100%
+    voltage_4v = battery_voltage(3742)
+    percent_4v = arduino_map(int(voltage_4v * 1000), 3000, 4200, 0, 100)
+    assert percent_4v == 100
+    
+    # 3.6V (3207 ADC) = 49% (due to integer math in map())
+    voltage_36v = battery_voltage(3207)
+    percent_36v = arduino_map(int(voltage_36v * 1000), 3000, 4200, 0, 100)
+    assert percent_36v == 49
+
+
+def test_moisture_percentage_clamping():
+    """Test that moisture percentage stays within valid bounds."""
+    # Test with values outside normal range
+    assert moisture_percentage(-100) == pytest.approx(102.4420, rel=0.001)
+    assert moisture_percentage(5000) == pytest.approx(-22.1001, rel=0.001)
+
+
+def test_arduino_map_helper():
+    """Test the Arduino map() re-implementation."""
+    assert arduino_map(512, 0, 1023, 0, 255) == 127
+    assert arduino_map(0, 0, 1023, 0, 255) == 0
+    assert arduino_map(1023, 0, 1023, 0, 255) == 255
+    assert arduino_map(200, 0, 4095, 0, 100) == 4
+
+
+def test_arduino_constrain_helper():
+    """Test the Arduino constrain() re-implementation."""
+    assert arduino_constrain(5, 0, 10) == 5
+    assert arduino_constrain(-5, 0, 10) == 0
+    assert arduino_constrain(15, 0, 10) == 10
+
+
+def test_combined_moisture_and_battery_logic():
+    """Test combined moisture and battery calculations."""
+    # Simulate a reading scenario
+    moisture_analog = 2500
+    battery_analog = 3200
+    
+    moisture_pct = moisture_percentage(moisture_analog)
+    battery_v = battery_voltage(battery_analog)
+    
+    # Verify moisture is around 39%
+    assert moisture_pct == pytest.approx(38.9499, rel=0.001)
+    
+    # Verify battery is around 3.59V
+    assert battery_v == pytest.approx(3.5917, rel=0.001)
+
+
+def test_sensor_calibration_values():
+    """Test with typical sensor calibration values."""
+    # Dry air reading (typical): ~800-1000
+    assert moisture_percentage(800) == pytest.approx(80.4884, rel=0.001)
+    assert moisture_percentage(1000) == pytest.approx(75.5555, rel=0.001)
+    
+    # Water reading (typical): ~2000-2500
+    assert moisture_percentage(2000) == pytest.approx(51.1700, rel=0.001)
+    assert moisture_percentage(2200) == pytest.approx(46.2759, rel=0.001)