diff --git a/gpt/__init__.py b/gpt/__init__.py
index d52a765..789c575 100644
--- a/gpt/__init__.py
+++ b/gpt/__init__.py
@@ -142,7 +142,7 @@ def calculate_header_crc32(self):
                                   self.number_of_partition_entries,
                                   self.size_of_partition_entry,
                                   self.partition_entry_array_crc32)
-        return binascii.crc32(header_crc32_input)
+        return binascii.crc32(header_crc32_input) & 0xffffffff
 
 
 class GPTPartitionEntry():
@@ -172,22 +172,22 @@ def is_empty(self):
 
 
 def calculate_partition_entry_array_crc32(data):
-    return binascii.crc32(data)
+    return binascii.crc32(data) & 0xffffffff
 
 
 def encode_mbr(mbr):
-    partition_record = bytes()
+    partition_record = bytearray()
     for i in range(0, 4):
-        partition = input.partitions[i]
-        partition_record.append(pack('< B B B B B B B B I I',
+        partition = mbr.partitions[i]
+        partition_record.extend(pack('< B B B B B B B B I I',
                                      partition.boot_indicator,
-                                     partition.start_chs[0],
                                      partition.start_chs[1],
                                      partition.start_chs[2],
+                                     partition.start_chs[0],
                                      partition.os_type,
-                                     partition.end_chs[0],
                                      partition.end_chs[1],
                                      partition.end_chs[2],
+                                     partition.end_chs[0],
                                      partition.lba_ss[0],
                                      partition.lba_ss[1]))
 
@@ -195,7 +195,7 @@ def encode_mbr(mbr):
                   mbr.bootstrap_code,
                   mbr.unique_mbr_disk_signature,
                   mbr.unknown,
-                  partition_record,
+                  bytes(partition_record),
                   mbr.signature)
     return output
 
@@ -298,9 +298,9 @@ def encode_gpt_partition_entry(gpt_partition_entry):
     data = pack('<16s 16s Q Q Q 72s',
             gpt_partition_entry.partition_type_guid_raw,
             gpt_partition_entry.unique_partition_guid_raw,
-            gpt_partition_entry.start_lba,
+            gpt_partition_entry.starting_lba,
             gpt_partition_entry.ending_lba,
-            gpt_partition_entry.attributes,
+            gpt_partition_entry.attributes_raw,
             gpt_partition_entry.partition_name_raw)
     return data
 
@@ -322,14 +322,14 @@ def decode_gpt_partition_entry(data):
 
 
 def encode_gpt_partition_entry_array(gpt_partition_entries, size, count):
-    data = bytes()
+    data = bytearray()
     for i in range(0, count):
         d = encode_gpt_partition_entry(gpt_partition_entries[i])
-        data.append(d)
+        data.extend(d)
         # fill with zeroes if less than size
         if len(d) < size:
-            data.append(bytes(size - len(d)))
-    return data
+            data.extend(bytearray(size - len(d)))
+    return bytes(data)
 
 
 def decode_gpt_partition_entry_array(data, size, count):
diff --git a/setup.cfg b/setup.cfg
index fc0cddd..3feb1f9 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -26,9 +26,14 @@ classifiers =
 zip_safe = False
 packages = gpt
 include_package_data = True
+setup_requires = pytest-runner
+tests_require = pytest
 
 [options.entry_points]
 console_scripts = 
   print_mbr=gpt.scripts:print_mbr
   print_gpt_header=gpt.scripts:print_gpt_header
   print_gpt_partition_entry_array=gpt.scripts:print_gpt_partition_entry_array
+
+[aliases]
+test=pytest
diff --git a/tests/sample-data/disk1.bin b/tests/sample-data/disk1.bin
new file mode 100644
index 0000000..07c43a7
Binary files /dev/null and b/tests/sample-data/disk1.bin differ
diff --git a/tests/sample-data/disk2.bin b/tests/sample-data/disk2.bin
new file mode 100644
index 0000000..c6dc714
Binary files /dev/null and b/tests/sample-data/disk2.bin differ
diff --git a/tests/sample-data/merged.bin b/tests/sample-data/merged.bin
new file mode 100644
index 0000000..5d9e681
Binary files /dev/null and b/tests/sample-data/merged.bin differ
diff --git a/tests/test_gpt.py b/tests/test_gpt.py
new file mode 100644
index 0000000..0da8f8e
--- /dev/null
+++ b/tests/test_gpt.py
@@ -0,0 +1,113 @@
+import pytest
+import os
+
+
+def load_sample_data(name):
+    path = os.path.join(os.path.dirname(__file__),
+                        'sample-data', '%s.bin' % (name,))
+    with open(path, 'rb') as f:
+        return f.read()
+
+
+def entries_range(h):
+    start = h.partition_entry_lba * 0x200
+    length = h.number_of_partition_entries * h.size_of_partition_entry
+    end = start + length
+    return start, end
+
+
+def test_roundtrip_mbr():
+    import gpt
+    sample = load_sample_data('disk1')
+    raw1 = sample[:0x200]
+    m = gpt.decode_mbr(raw1)
+    assert m.is_valid()
+    raw2 = gpt.encode_mbr(m)
+    assert raw1 == raw2
+
+
+def test_roundtrip_gpt_header():
+    import gpt
+    sample = load_sample_data('disk1')
+    raw1 = sample[0x200:0x400]
+    h = gpt.decode_gpt_header(raw1)
+    assert h.header_size == 92, "expected header size 92"
+    raw2 = gpt.encode_gpt_header(h)
+    assert raw1[:h.header_size] == raw2
+
+
+def test_roundtrip_gpt_partition_entry_array():
+    import gpt
+    sample = load_sample_data('disk1')
+    h = gpt.decode_gpt_header(sample[0x200:0x400])
+
+    start, end = entries_range(h)
+
+    decoded_entries = gpt.decode_gpt_partition_entry_array(
+        sample[start:end],
+        h.size_of_partition_entry,
+        h.number_of_partition_entries)
+
+    reencoded_entries = gpt.encode_gpt_partition_entry_array(
+        decoded_entries,
+        h.size_of_partition_entry,
+        h.number_of_partition_entries)
+
+    assert sample[start:end] == reencoded_entries
+
+
+def test_merge():
+    import gpt
+
+    sample1 = load_sample_data('disk1')
+    sample2 = load_sample_data('disk2')
+    sample_merged = load_sample_data('merged')
+
+    h1 = gpt.decode_gpt_header(sample1[0x200:0x400])
+    h2 = gpt.decode_gpt_header(sample2[0x200:0x400])
+
+    start1, end1 = entries_range(h1)
+    start2, end2 = entries_range(h2)
+
+    decoded_entries1 = gpt.decode_gpt_partition_entry_array(
+        sample1[start1:end1],
+        h1.size_of_partition_entry,
+        h1.number_of_partition_entries)
+
+    decoded_entries2 = gpt.decode_gpt_partition_entry_array(
+        sample2[start2:end2],
+        h2.size_of_partition_entry,
+        h2.number_of_partition_entries)
+
+    # Copy disk2 partition table
+    merged_h = gpt.decode_gpt_header(sample2[0x200:0x400])
+    merged_entries = list(decoded_entries2)
+
+    # Copy partitions 1-4 from disk1
+    merged_entries[0:4] = decoded_entries1[0:4]
+    merged_entries_raw = gpt.encode_gpt_partition_entry_array(
+        merged_entries,
+        merged_h.size_of_partition_entry,
+        merged_h.number_of_partition_entries)
+
+    # Update crc32 values
+    merged_h.partition_entry_array_crc32 = gpt.calculate_partition_entry_array_crc32(merged_entries_raw)
+    merged_h.header_crc32 = merged_h.calculate_header_crc32()
+
+    # Should be valid
+    assert merged_h.is_valid()
+
+    # Encode header
+    merged_h_raw = gpt.encode_gpt_header(merged_h)
+
+    m_start, m_end = entries_range(merged_h)
+    assert m_end - m_start == len(merged_entries_raw)
+
+    # Construct the new partition table
+    merged_raw = bytearray(0x400)
+    merged_raw[:0x200] = sample1[:0x200]    # Copy protective MBR from disk1
+    merged_raw[0x200:0x200+merged_h.header_size] = merged_h_raw
+    merged_raw[m_start:m_end] = merged_entries_raw
+
+    # Did we get what we expect?
+    assert merged_raw == sample_merged
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..52065f2
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,7 @@
+[tox]
+envlist = py27,py37
+
+[testenv]
+commands = pytest
+deps =
+    pytest