And now with system tests.

tests/system/conftest.py

@@ -0,0 +1,35 @@
+import pytest
+import socket
+import struct
+from threading import Thread
+
+from server import app
+
+
+@pytest.fixture(autouse=True, scope="module")
+def server(request):
+    t = Thread(target=app.serve_forever)
+    t.start()
+
+    def fin():
+        app.shutdown()
+        app.server_close()
+        t.join()
+
+    request.addfinalizer(fin)
+    return app
+
+
+@pytest.yield_fixture
+def sock(server):
+    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    sock.connect(server.socket.getsockname())
+
+    yield sock
+
+    sock.close()
+
+
+@pytest.fixture
+def mbap():
+    return struct.pack('>HHHB', 0, 0, 6, 1)

tests/system/server.py

@@ -0,0 +1,13 @@
+from umodbus import get_server
+
+app = get_server('localhost', 0)
+
+
+@app.route(slave_ids=[1], function_codes=[1, 2], addresses=list(range(0, 10)))
+def read_coils(slave_id, address):
+    return address % 2
+
+
+@app.route(slave_ids=[1], function_codes=[1, 2], addresses=[666])
+def failure(slave_id, address):
+    raise Exception

tests/system/test_functions.py

@@ -0,0 +1,123 @@
+import pytest
+import struct
+
+
+def validate_transaction_id(request_mbap, response):
+    """ Check if Transaction id in request and response is equal. """
+    assert struct.unpack('>H', request_mbap[:2]) == \
+        struct.unpack('>H', response[:2])
+
+
+def validate_protocol_id(request_mbap, response):
+    """ Check if Protocol id in request and response is equal. """
+    assert struct.unpack('>H', request_mbap[2:4]) == \
+        struct.unpack('>H', response[2:4])
+
+
+def validate_length(response):
+    """ Check if Length field contains actual length of response. """
+    assert struct.unpack('>H', response[4:6])[0] == len(response[6:])
+
+
+def validate_unit_id(request_mbap, response):
+    """ Check if Unit id in request and response is equal. """
+    assert struct.unpack('>B', request_mbap[6:7]) == \
+        struct.unpack('>B', response[6:7])
+
+
+def validate_response_mbap(request_mbap, response):
+    """ Validate if fields in response MBAP contain correct values. """
+    validate_transaction_id(request_mbap, response)
+    validate_protocol_id(request_mbap, response)
+    validate_length(response)
+    validate_unit_id(request_mbap, response)
+
+
+def validate_function_code(request, response):
+    """ Validate if Function code in request and response equal. """
+    assert struct.unpack('>B', request[7:8])[0] == \
+        struct.unpack('>B', response[7:8])[0]
+
+
+def validate_byte_count(request, response):
+    """ Check of byte count field contains actual byte count and if byte count
+    matches with the amount of requests quantity.
+    """
+    byte_count = struct.unpack('>B', response[8:9])[0]
+
+    quantity = struct.unpack('>H', request[-2:])[0]
+    expected_byte_count = quantity // 8
+
+    if quantity % 8 != 0:
+        expected_byte_count = (quantity // 8) + 1
+
+    assert byte_count == len(response[9:])
+    assert byte_count == expected_byte_count
+
+
+def unpack_single_bit_values(response):
+    byte_count = struct.unpack('>B', response[8:9])[0]
+
+    fmt = '>' + ('B' * byte_count)
+    return struct.unpack(fmt, response[9:])
+
+
+def test_read_coils_successfully(sock, mbap):
+    """ Validate response PDU of a succesful request. """
+    function_code, starting_address, quantity = (1, 0, 10)
+    adu = mbap + struct.pack('>BHH', function_code, starting_address, quantity)
+
+    sock.send(adu)
+    resp = sock.recv(1024)
+
+    validate_response_mbap(mbap, resp)
+    validate_function_code(adu, resp)
+    validate_byte_count(adu, resp)
+
+    assert unpack_single_bit_values(resp) == (170, 2)
+
+
+@pytest.mark.parametrize('quantity', [
+    0,
+    0x07D0 + 1,
+])
+def test_read_coils_with_invalid_addres(sock, mbap, quantity):
+    """ Validate response PDU of request returning excpetion response with
+    error code 3.
+    """
+    function_code, starting_address, quantity = (1, 0, quantity)
+    adu = mbap + struct.pack('>BHH', function_code, starting_address, quantity)
+
+    sock.send(adu)
+    resp = sock.recv(1024)
+
+    validate_response_mbap(mbap, resp)
+    assert struct.unpack('>BB', resp[-2:]) == (0x81, 3)
+
+
+def test_read_coils_with_invalid_value(sock, mbap):
+    """ Validate response PDU of request returning excpetion response with
+    error code 2.
+    """
+    function_code, starting_address, quantity = (1, 9, 2)
+    adu = mbap + struct.pack('>BHH', function_code, starting_address, quantity)
+
+    sock.send(adu)
+    resp = sock.recv(1024)
+
+    validate_response_mbap(mbap, resp)
+    assert struct.unpack('>BB', resp[-2:]) == (0x81, 2)
+
+
+def test_read_coils_with_server_failure(sock, mbap):
+    """ Validate response PDU of request returning excpetion response with
+    error code 2.
+    """
+    function_code, starting_address, quantity = (1, 666, 1)
+    adu = mbap + struct.pack('>BHH', function_code, starting_address, quantity)
+
+    sock.send(adu)
+    resp = sock.recv(1024)
+
+    validate_response_mbap(mbap, resp)
+    assert struct.unpack('>BB', resp[-2:]) == (0x81, 4)