nettest: Add a guide document for the nettest directory.

Signed-off-by: zhangshuai39 <zhangshuai39@xiaomi.com>

Documentation/applications/testing/nettest/index.rst

@@ -0,0 +1,93 @@
+================
+Net Test Module
+================
+
+The ``apps/testing/nettest`` directory is used to build testcases related
+to the network protocol stack. You can use it on any device with network
+protocol stack capabilities.
+
+Directory Structure
+===================
+
+::
+
+    ├──tcp
+    │  ├── test_tcp_connect_ipv4.c  # The testcase of TCP connect
+    │  ├── ...
+    │  ├── test_tcp_common.c        # TCP testcase common function
+    │  ├── test_tcp.h               # TCP testcases declaration
+    │  └── test_tcp.c               # TCP testcase execution entry
+    ├──udp
+    │  ├── ...
+    │  ├── test_udp.h               # UDP testcases declaration
+    │  └── test_udp.c               # UDP testcase execution entry
+    ├── ...
+    ├──utils                        # Utils for testcases
+    │  ├── ...
+    │  ├── nettest_netdump.c
+    │  ├── nettest_tcpserver.c
+    │  └── utils.h
+    ├── CmakeLists.txt
+    ├── Kconfig                     # Enable module testcases
+    ├── Make.defs
+    └── Makefile
+
+How to Build
+============
+
+Firstly, all testcases in this directory rely on the cmocka framework,
+so please ensure that the following cmocka configuration is turned on:
+
+- ``CONFIG_ALLOW_MIT_COMPONENTS=y``
+- ``CONFIG_LIBC_REGEX=y``
+- ``CONFIG_TESTING_CMOCKA=y``
+
+Then, open the network part testcase configuration:
+
+- ``CONFIG_TESTING_NET_TEST=y``
+
+Finally, you can choose which protocol testcase to enable through
+configuration. Some protocol configurations depend on other network
+configurations; you can view the dependencies in the ``Kconfig`` file. Take
+the TCP testcase as an example:
+
+- ``CONFIG_NET_TCPBACKLOG=y``  – TCP testcase compilation dependencies
+- ``CONFIG_NET_TCP=y``         – TCP testcase compilation dependencies
+- ``CONFIG_TESTING_NET_TCP=y`` – TCP testcase configuration items; for other
+  protocols, just replace the trailing protocol name
+
+How to Run
+==========
+
+After the testcase is built, you can run the testcase at the command line through
+the following commands:
+
+- ``cmocka --test test_tcp_connect_ipv4`` – Run a single testcase
+
+- ``cmocka_net_tcp`` – Run TCP testcase (for other protocols, just replace
+  the trailing protocol name)
+
+In addition, when you run ``cmocka``, the above commands will also be included.
+
+How to Add Testcases
+====================
+
+If you want to add testcases, please follow these steps:
+
+1. Add the testcase source file to the corresponding directory. Please follow
+   the following naming rules for source files:
+
+   ``test_<protocol>_<function description>_<additional description>.c``
+
+   For example: ``test_tcp_connect_ipv4.c``
+
+   Test case names are the same as source files, such as ``test_tcp_connect_ipv4()``.
+
+2. Add the testcase source file to the ``CMakeLists.txt`` file.
+
+3. Add the testcase source file to the ``Makefile`` file.
+
+4. Add the testcase to the corresponding declaration file and execute entry file.
+   For example, ``test_tcp_connect_ipv4()`` needs to be added to ``test_tcp.h``
+   and ``test_tcp.c``. If you have a separate setup function, also add it to
+   the above two files.