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+.. _unittest: https://docs.python.org/2/library/unittest.html
+.. _TestCase: https://docs.python.org/2/library/unittest.html#unittest.TestCase
+.. _AssertionError: https://docs.python.org/2/library/exceptions.html#exceptions.AssertionError
+.. _SkipTest: https://docs.python.org/2/library/unittest.html#unittest.SkipTest
+.. _virtualenv: http://docs.python-guide.org/en/latest/dev/virtualenvs/
+.. _scapy: http://www.secdev.org/projects/scapy/
+.. _logging: https://docs.python.org/2/library/logging.html
+.. _process: https://docs.python.org/2/library/multiprocessing.html#the-process-class
+.. _pipes: https://docs.python.org/2/library/multiprocessing.html#multiprocessing.Pipe
+.. _managed: https://docs.python.org/2/library/multiprocessing.html#managers
+
+.. |vtf| replace:: VPP Test Framework
+
+|vtf|
+=====
+
+.. contents::
+   :local:
+   :depth: 1
+
+Overview
+########
+
+The goal of the |vtf| is to ease writing, running and debugging
+unit tests for the VPP. For this, python was chosen as a high level language
+allowing rapid development with scapy_ providing the necessary tool for creating
+and dissecting packets.
+
+Anatomy of a test case
+######################
+
+Python's unittest_ is used as the base framework upon which the VPP test
+framework is built. A test suite in the |vtf| consists of multiple classes
+derived from `VppTestCase`, which is itself derived from TestCase_.
+The test class defines one or more test functions, which act as test cases.
+
+Function flow when running a test case is:
+
+1. `setUpClass <VppTestCase.setUpClass>`:
+   This function is called once for each test class, allowing a one-time test
+   setup to be executed. If this functions throws an exception,
+   none of the test functions are executed.
+2. `setUp <VppTestCase.setUp>`:
+   The setUp function runs before each of the test functions. If this function
+   throws an exception other than AssertionError_ or SkipTest_, then this is
+   considered an error, not a test failure.
+3. *test_<name>*:
+   This is the guts of the test case. It should execute the test scenario
+   and use the various assert functions from the unittest framework to check
+   necessary. Multiple test_<name> methods can exist in a test case.
+4. `tearDown <VppTestCase.tearDown>`:
+   The tearDown function is called after each test function with the purpose
+   of doing partial cleanup.
+5. `tearDownClass <VppTestCase.tearDownClass>`:
+   Method called once after running all of the test functions to perform
+   the final cleanup.
+
+Logging
+#######
+
+Each test case has a logger automatically created for it, stored in
+'logger' property, based on logging_. Use the logger's standard methods
+debug(), info(), error(), ... to emit log messages to the logger.
+
+All the log messages go always into a log file in temporary directory
+(see below).
+
+To control the messages printed to console, specify the V= parameter.
+
+.. code-block:: shell
+
+   make test         # minimum verbosity
+   make test V=1     # moderate verbosity
+   make test V=2     # maximum verbosity
+
+Parallel test execution
+#######################
+
+|vtf| test suites can be run in parallel. Each test suite is executed
+in a separate process spawned by Python multiprocessing process_.
+
+The results from child test suites are sent to parent through pipes_, which are
+aggregated and summarized at the end of the run.
+
+Stdout, stderr and logs logged in child processes are redirected to individual
+parent managed_ queues. The data from these queues are then emitted to stdout
+of the parent process in the order the test suites have finished. In case there
+are no finished test suites (such as at the beginning of the run), the data
+from last started test suite are emitted in real time.
+
+To enable parallel test run, specify the number of parallel processes:
+
+.. code-block:: shell
+
+   make test TEST_JOBS=n       # at most n processes will be spawned
+   make test TEST_JOBS=auto    # chosen based on the number of cores
+                               # and the size of shared memory
+
+Test temporary directory and VPP life cycle
+###########################################
+
+Test separation is achieved by separating the test files and vpp instances.
+Each test creates a temporary directory and it's name is used to create
+a shared memory prefix which is used to run a VPP instance.
+The temporary directory name contains the testcase class name for easy
+reference, so for testcase named 'TestVxlan' the directory could be named
+e.g. vpp-unittest-TestVxlan-UNUP3j.
+This way, there is no conflict between any other VPP instances running
+on the box and the test VPP. Any temporary files created by the test case
+are stored in this temporary test directory.
+
+The test temporary directory holds the following interesting files:
+
+* log.txt - this contains the logger output on max verbosity
+* pg*_in.pcap - last injected packet stream into VPP, named after the interface,
+  so for pg0, the file will be named pg0_in.pcap
+* pg*_out.pcap - last capture file created by VPP for interface, similarly,
+  named after the interface, so for e.g. pg1, the file will be named
+  pg1_out.pcap
+* history files - whenever the capture is restarted or a new stream is added,
+  the existing files are rotated and renamed, so all the pcap files
+  are always saved for later debugging if needed
+* core - if vpp dumps a core, it'll be stored in the temporary directory
+* vpp_stdout.txt - file containing output which vpp printed to stdout
+* vpp_stderr.txt - file containing output which vpp printed to stderr
+
+*NOTE*: existing temporary directories named vpp-unittest-* are automatically
+removed when invoking 'make test*' or 'make retest*' to keep the temporary
+directory clean.
+
+Virtual environment
+###################
+
+Virtualenv_ is a python module which provides a means to create an environment
+containing the dependencies required by the |vtf|, allowing a separation
+from any existing system-wide packages. |vtf|'s Makefile automatically
+creates a virtualenv_ inside build-root and installs the required packages
+in that environment. The environment is entered whenever executing a test
+via one of the make test targets.
+
+Naming conventions
+##################
+
+Most unit tests do some kind of packet manipulation - sending and receiving
+packets between VPP and virtual hosts connected to the VPP. Referring
+to the sides, addresses, etc. is always done as if looking from the VPP side,
+thus:
+
+* *local_* prefix is used for the VPP side.
+  So e.g. `local_ip4 <VppInterface.local_ip4>` address is the IPv4 address
+  assigned to the VPP interface.
+* *remote_* prefix is used for the virtual host side.
+  So e.g. `remote_mac <VppInterface.remote_mac>` address is the MAC address
+  assigned to the virtual host connected to the VPP.
+
+Automatically generated addresses
+#################################
+
+To send packets, one needs to typically provide some addresses, otherwise
+the packets will be dropped. The interface objects in |vtf| automatically
+provide addresses based on (typically) their indexes, which ensures
+there are no conflicts and eases debugging by making the addressing scheme
+consistent.
+
+The developer of a test case typically doesn't need to work with the actual
+numbers, rather using the properties of the objects. The addresses typically
+come in two flavors: '<address>' and '<address>n' - note the 'n' suffix.
+The former address is a Python string, while the latter is translated using
+socket.inet_pton to raw format in network byte order - this format is suitable
+for passing as an argument to VPP APIs.
+
+e.g. for the IPv4 address assigned to the VPP interface:
+
+* local_ip4 - Local IPv4 address on VPP interface (string)
+* local_ip4n - Local IPv4 address - raw, suitable as API parameter.
+
+These addresses need to be configured in VPP to be usable using e.g.
+`VppInterface.config_ip4` API. Please see the documentation to
+`VppInterface` for more details.
+
+By default, there is one remote address of each kind created for L3:
+remote_ip4 and remote_ip6. If the test needs more addresses, because it's
+simulating more remote hosts, they can be generated using
+`generate_remote_hosts` API and the entries for them inserted into the ARP
+table using `configure_ipv4_neighbors` API.
+
+Packet flow in the |vtf|
+########################
+
+Test framework -> VPP
+~~~~~~~~~~~~~~~~~~~~~
+
+|vtf| doesn't send any packets to VPP directly. Traffic is instead injected
+using packet-generator interfaces, represented by the `VppPGInterface` class.
+Packets are written into a temporary .pcap file, which is then read by the VPP
+and the packets are injected into the VPP world.
+
+To add a list of packets to an interface, call the `VppPGInterface.add_stream`
+method on that interface. Once everything is prepared, call `pg_start` method to
+start the packet generator on the VPP side.
+
+VPP -> test framework
+~~~~~~~~~~~~~~~~~~~~~
+
+Similarly, VPP doesn't send any packets to |vtf| directly. Instead, packet
+capture feature is used to capture and write traffic to a temporary .pcap file,
+which is then read and analyzed by the |vtf|.
+
+The following APIs are available to the test case for reading pcap files.
+
+* `VppPGInterface.get_capture`: this API is suitable for bulk & batch
+  style of test, where a list of packets is prepared & sent, then the
+  received packets are read and verified. The API needs the number of
+  packets which are expected to be captured (ignoring filtered
+  packets - see below) to know when the pcap file is completely
+  written by the VPP. If using packet infos for verifying packets,
+  then the counts of the packet infos can be automatically used by
+  `VppPGInterface.get_capture` to get the proper count (in this case
+  the default value None can be supplied as expected_count or omitted
+  altogether).
+* `VppPGInterface.wait_for_packet`: this API is suitable for
+  interactive style of test, e.g. when doing session management,
+  three-way handshakes, etc. This API waits for and returns a single
+  packet, keeping the capture file in place and remembering
+  context. Repeated invocations return following packets (or raise
+  Exception if timeout is reached) from the same capture file (=
+  packets arriving on the same interface).
+
+*NOTE*: it is not recommended to mix these APIs unless you understand
+how they work internally. None of these APIs rotate the pcap capture
+file, so calling e.g. `VppPGInterface.get_capture` after
+`VppPGInterface.wait_for_packet` will return already read packets.  It
+is safe to switch from one API to another after calling
+`VppPGInterface.enable_capture` as that API rotates the capture file.
+
+Automatic filtering of packets:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Both APIs (`VppPGInterface.get_capture` and
+`VppPGInterface.wait_for_packet`) by default filter the packet
+capture, removing known uninteresting packets from it - these are IPv6
+Router Advertisements and IPv6 Router Alerts. These packets are
+unsolicited and from the point of |vtf| are random. If a test wants
+to receive these packets, it should specify either None or a custom
+filtering function as the value to the 'filter_out_fn' argument.
+
+Common API flow for sending/receiving packets:
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+We will describe a simple scenario, where packets are sent from pg0 to pg1
+interface, assuming that the interfaces were created using
+`create_pg_interfaces` API.
+
+1. Create a list of packets for pg0::
+
+     packet_count = 10
+     packets = create_packets(src=self.pg0, dst=self.pg1,
+                              count=packet_count)
+
+2. Add that list of packets to the source interface::
+
+     self.pg0.add_stream(packets)
+
+3. Enable capture on the destination interface::
+
+     self.pg1.enable_capture()
+
+4. Start the packet generator::
+
+     self.pg_start()
+
+5. Wait for capture file to appear and read it::
+
+     capture = self.pg1.get_capture(expected_count=packet_count)
+
+6. Verify packets match sent packets::
+
+     self.verify_capture(send=packets, captured=capture)
+
+Test framework objects
+######################
+
+The following objects provide VPP abstraction and provide a means to do
+common tasks easily in the test cases.
+
+* `VppInterface`: abstract class representing generic VPP interface
+  and contains some common functionality, which is then used by derived classes
+* `VppPGInterface`: class representing VPP packet-generator interface.
+  The interface is created/destroyed when the object is created/destroyed.
+* `VppSubInterface`: VPP sub-interface abstract class, containing common
+  functionality for e.g. `VppDot1QSubint` and `VppDot1ADSubint` classes
+
+How VPP APIs/CLIs are called
+############################
+
+Vpp provides python bindings in a python module called vpp-papi, which the test
+framework installs in the virtual environment. A shim layer represented by
+the `VppPapiProvider` class is built on top of the vpp-papi, serving these
+purposes:
+
+1. Automatic return value checks:
+   After each API is called, the return value is checked against the expected
+   return value (by default 0, but can be overridden) and an exception
+   is raised if the check fails.
+2. Automatic call of hooks:
+
+   a. `before_cli <Hook.before_cli>` and `before_api <Hook.before_api>` hooks
+      are used for debug logging and stepping through the test
+   b. `after_cli <Hook.after_cli>` and `after_api <Hook.after_api>` hooks
+      are used for monitoring the vpp process for crashes
+3. Simplification of API calls:
+   Many of the VPP APIs take a lot of parameters and by providing sane defaults
+   for these, the API is much easier to use in the common case and the code is
+   more readable. E.g. ip_add_del_route API takes ~25 parameters, of which
+   in the common case, only 3 are needed.
+
+Utility methods
+###############
+
+Some interesting utility methods are:
+
+* `ppp`: 'Pretty Print Packet' - returns a string containing the same output
+  as Scapy's packet.show() would print
+* `ppc`: 'Pretty Print Capture' - returns a string containing printout of
+  a capture (with configurable limit on the number of packets printed from it)
+  using `ppp`
+
+*NOTE*: Do not use Scapy's packet.show() in the tests, because it prints
+the output to stdout. All output should go to the logger associated with
+the test case.
+
+Example: how to add a new test
+##############################
+
+In this example, we will describe how to add a new test case which tests
+basic IPv4 forwarding.
+
+1. Add a new file called test_ip4_fwd.py in the test directory, starting
+   with a few imports::
+
+     from framework import VppTestCase
+     from scapy.layers.l2 import Ether
+     from scapy.packet import Raw
+     from scapy.layers.inet import IP, UDP
+     from random import randint
+
+2. Create a class inherited from the VppTestCase::
+
+     class IP4FwdTestCase(VppTestCase):
+         """ IPv4 simple forwarding test case """
+
+3. Add a setUpClass function containing the setup needed for our test to run::
+
+         @classmethod
+         def setUpClass(self):
+             super(IP4FwdTestCase, self).setUpClass()
+             self.create_pg_interfaces(range(2))  #  create pg0 and pg1
+             for i in self.pg_interfaces:
+                 i.admin_up()  # put the interface up
+                 i.config_ip4()  # configure IPv4 address on the interface
+                 i.resolve_arp()  # resolve ARP, so that we know VPP MAC
+
+4. Create a helper method to create the packets to send::
+
+         def create_stream(self, src_if, dst_if, count):
+             packets = []
+             for i in range(count):
+                 # create packet info stored in the test case instance
+                 info = self.create_packet_info(src_if, dst_if)
+                 # convert the info into packet payload
+                 payload = self.info_to_payload(info)
+                 # create the packet itself
+                 p = (Ether(dst=src_if.local_mac, src=src_if.remote_mac) /
+                      IP(src=src_if.remote_ip4, dst=dst_if.remote_ip4) /
+                      UDP(sport=randint(1000, 2000), dport=5678) /
+                      Raw(payload))
+                 # store a copy of the packet in the packet info
+                 info.data = p.copy()
+                 # append the packet to the list
+                 packets.append(p)
+
+             # return the created packet list
+             return packets
+
+5. Create a helper method to verify the capture::
+
+         def verify_capture(self, src_if, dst_if, capture):
+             packet_info = None
+             for packet in capture:
+                 try:
+                     ip = packet[IP]
+                     udp = packet[UDP]
+                     # convert the payload to packet info object
+                     payload_info = self.payload_to_info(packet[Raw])
+                     # make sure the indexes match
+                     self.assert_equal(payload_info.src, src_if.sw_if_index,
+                                       "source sw_if_index")
+                     self.assert_equal(payload_info.dst, dst_if.sw_if_index,
+                                       "destination sw_if_index")
+                     packet_info = self.get_next_packet_info_for_interface2(
+                                       src_if.sw_if_index,
+                                       dst_if.sw_if_index,
+                                       packet_info)
+                     # make sure we didn't run out of saved packets
+                     self.assertIsNotNone(packet_info)
+                     self.assert_equal(payload_info.index, packet_info.index,
+                                       "packet info index")
+                     saved_packet = packet_info.data  # fetch the saved packet
+                     # assert the values match
+                     self.assert_equal(ip.src, saved_packet[IP].src,
+                                       "IP source address")
+                     # ... more assertions here
+                     self.assert_equal(udp.sport, saved_packet[UDP].sport,
+                                       "UDP source port")
+                 except:
+                     self.logger.error(ppp("Unexpected or invalid packet:",
+                                       packet))
+                     raise
+             remaining_packet = self.get_next_packet_info_for_interface2(
+                        src_if.sw_if_index,
+                        dst_if.sw_if_index,
+                        packet_info)
+             self.assertIsNone(remaining_packet,
+                               "Interface %s: Packet expected from interface "
+                               "%s didn't arrive" % (dst_if.name, src_if.name))
+
+6. Add the test code to test_basic function::
+
+         def test_basic(self):
+             count = 10
+             # create the packet stream
+             packets = self.create_stream(self.pg0, self.pg1, count)
+             # add the stream to the source interface
+             self.pg0.add_stream(packets)
+             # enable capture on both interfaces
+             self.pg0.enable_capture()
+             self.pg1.enable_capture()
+             # start the packet generator
+             self.pg_start()
+             # get capture - the proper count of packets was saved by
+             # create_packet_info() based on dst_if parameter
+             capture = self.pg1.get_capture()
+             # assert nothing captured on pg0 (always do this last, so that
+             # some time has already passed since pg_start())
+             self.pg0.assert_nothing_captured()
+             # verify capture
+             self.verify_capture(self.pg0, self.pg1, capture)
+
+7. Run the test by issuing 'make test' or, to run only this specific
+   test, issue 'make test TEST=test_ip4_fwd'.