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diff --git a/Adafruit_Python_GPIO/tests/test_I2C.py b/Adafruit_Python_GPIO/tests/test_I2C.py
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+++ b/Adafruit_Python_GPIO/tests/test_I2C.py
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+# Copyright (c) 2014 Adafruit Industries
+# Author: Tony DiCola
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+import logging
+import unittest
+
+from mock import Mock, patch
+
+import Adafruit_GPIO.Platform as Platform
+
+
+# Enable debug logging to stdout during tests.
+logging.basicConfig()
+logging.getLogger().setLevel(logging.DEBUG)
+
+
+class MockSMBus(object):
+    # Mock the smbus.SMBus class to record all data written to specific
+    # addresses and registers in the _written member.
+    def __init__(self):
+        # _written will store a dictionary of address to register dictionary.
+        # Each register dictionary will store a mapping of register value to
+        # an array of all written values (in sequential write order).
+        self._written = {}
+        self._read = {}
+
+    def _write_register(self, address, register, value):
+        self._written.setdefault(address, {}).setdefault(register, []).append(value)
+
+    def _read_register(self, address, register):
+        return self._read.get(address).get(register).pop(0)
+
+    def write_byte_data(self, address, register, value):
+        self._write_register(address, register, value)
+
+    def write_word_data(self, address, register, value):
+        self._write_register(address, register, value >> 8 & 0xFF)
+        self._write_register(address, register+1, value & 0xFF)
+
+    def write_i2c_block_data(self, address, register, values):
+        for i, value in enumerate(values):
+            self._write_register(address, register+i, value & 0xFF)
+
+    def read_byte_data(self, address, register):
+        return self._read_register(address, register)
+
+    def read_word_data(self, address, register):
+        high = self._read_register(address, register)
+        low = self._read_register(address, register+1)
+        return (high << 8) | low
+
+    def read_i2c_block_data(self, address, length):
+        return [self._read_register(address+i) for i in range(length)]
+
+
+def create_device(address, busnum):
+    # Mock the smbus module and inject it into the global namespace so the
+    # Adafruit_GPIO.I2C module can be imported.  Also inject a mock SMBus
+    # instance to be returned by smbus.SMBus function calls.
+    smbus = Mock()
+    mockbus = MockSMBus()
+    smbus.SMBus.return_value = mockbus
+    with patch.dict('sys.modules', {'smbus': smbus}):
+        import Adafruit_GPIO.I2C as I2C
+        return (I2C.Device(address, busnum), smbus, mockbus)
+
+def safe_import_i2c():
+    # Mock the smbus module and inject it into the global namespace so the
+    # Adafruit_GPIO.I2C module can be imported.  The imported I2C module is
+    # returned so global functions can be called on it.
+    with patch.dict('sys.modules', {'smbus': Mock() }):
+        import Adafruit_GPIO.I2C as I2C
+        return I2C
+
+
+class TestI2CDevice(unittest.TestCase):
+
+    def test_address_and_bus_set_correctly(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        self.assertEqual(device._bus, mockbus)
+        smbus.SMBus.assert_called_with(1)
+        self.assertEqual(device._address, 0x1F)
+
+    def test_write8(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        device.write8(0xFE, 0xED)
+        self.assertDictEqual(mockbus._written, { 0x1F: { 0xFE: [0xED] }})
+
+    def test_write8_truncates_to_8bits(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        device.write8(0xFE, 0xBEEFED)
+        self.assertDictEqual(mockbus._written, { 0x1F: { 0xFE: [0xED] }})
+
+    def test_write16(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        device.write16(0xFE, 0xBEEF)
+        self.assertDictEqual(mockbus._written, { 0x1F: { 0xFE: [0xBE],
+                                                         0xFF: [0xEF] }})
+
+    def test_write16_truncates_to_8bits(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        device.write16(0xFE, 0xFEEDBEEF)
+        self.assertDictEqual(mockbus._written, { 0x1F: { 0xFE: [0xBE],
+                                                         0xFF: [0xEF] }})
+
+    def test_writeList(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        device.writeList(0x00, [0xFE, 0xED, 0xBE, 0xEF])
+        self.assertDictEqual(mockbus._written, { 0x1F: { 0x00: [0xFE],
+                                                         0x01: [0xED],
+                                                         0x02: [0xBE],
+                                                         0x03: [0xEF] }})
+
+    def test_readU8(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        mockbus._read[0x1F] = { 0xFE: [0xED] }
+        value = device.readU8(0xFE)
+        self.assertEqual(value, 0xED)
+
+    def test_readS8(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        mockbus._read[0x1F] = { 0xFE: [0xED] }
+        value = device.readS8(0xFE)
+        self.assertEqual(value, -19)
+
+    def test_readU16(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        mockbus._read[0x1F] = { 0xFE: [0xED], 0xFF: [0x01] }
+        value = device.readU16(0xFE)
+        self.assertEqual(value, 0xED01)
+
+    def test_readS16(self):
+        device, smbus, mockbus = create_device(0x1F, 1)
+        mockbus._read[0x1F] = { 0xFE: [0xED], 0xFF: [0x01] }
+        value = device.readS16(0xFE)
+        self.assertEqual(value, -4863)
+
+
+class TestGetDefaultBus(unittest.TestCase):
+    @patch('Adafruit_GPIO.Platform.pi_revision', Mock(return_value=1))
+    @patch('Adafruit_GPIO.Platform.platform_detect', Mock(return_value=Platform.RASPBERRY_PI))
+    def test_raspberry_pi_rev1(self):
+        I2C = safe_import_i2c()
+        bus = I2C.get_default_bus()
+        self.assertEqual(bus, 0)
+
+    @patch('Adafruit_GPIO.Platform.pi_revision', Mock(return_value=2))
+    @patch('Adafruit_GPIO.Platform.platform_detect', Mock(return_value=Platform.RASPBERRY_PI))
+    def test_raspberry_pi_rev2(self):
+        I2C = safe_import_i2c()
+        bus = I2C.get_default_bus()
+        self.assertEqual(bus, 1)
+
+    @patch('Adafruit_GPIO.Platform.platform_detect', Mock(return_value=Platform.BEAGLEBONE_BLACK))
+    def test_beaglebone_black(self):
+        I2C = safe_import_i2c()
+        bus = I2C.get_default_bus()
+        self.assertEqual(bus, 1)
+
+    @patch('Adafruit_GPIO.Platform.platform_detect', Mock(return_value=Platform.UNKNOWN))
+    def test_unknown(self):
+        I2C = safe_import_i2c()
+        self.assertRaises(RuntimeError, I2C.get_default_bus)