esp32: add unit testing doc

docs/index.rst

@@ -36,6 +36,7 @@ Contents:
    Secure Boot <security/secure-boot>
    Deep Sleep Wake Stubs <deep-sleep-stub>
    ULP Coprocessor <ulp>
+   Unit Testing <unit-tests>
 
 .. toctree::
    :caption: API Reference
@@ -77,5 +78,4 @@ Contents:
 Indices
 =======
 
-* :ref:`genindex`
-
+* :ref:`genindex`

docs/unit-tests.rst

@@ -0,0 +1,68 @@
+Unit Testing in ESP32
+=====================
+
+ESP-IDF comes with a unit test app based on Unity - unit test framework. Unit tests are integrated in the ESP-IDF repository and are placed in ``test`` subdirectory of each component respectively.
+
+Adding unit tests
+-----------------
+
+Unit tests are added in the ``test`` subdirectory of the respective component.
+Tests are added in C files, a single C file can include multiple test cases.
+Test files start with the word "test".
+
+The test file should include unity.h and the header for the C module to be tested.
+
+Tests are added in a function in the C file as follows::
+
+    TEST_CASE("test name", "[module name]"
+    {
+            // Add test here
+    }
+
+First argument is a descriptive name for the test, second argument is an identifier in square brackets.
+Identifiers are used to group related test, or tests with specific properties.
+
+There is no need to add a main function with ``UNITY_BEGIN()`` and ``​UNITY_END()`` in each test case.
+``unity_platform.c`` will run ``UNITY_BEGIN()``, run the tests cases, and then call ``​UNITY_END()``.
+
+Each `test` subdirectory needs to include component.mk file with at least the following line of code::
+
+    COMPONENT_ADD_LDFLAGS = -Wl,--whole-archive -l$(COMPONENT_NAME) -Wl,--no-whole-archive
+
+See http://www.throwtheswitch.org/unity for more information about writing tests in Unity.
+
+Building unit test app
+----------------------
+
+Follow the setup instructions in the top-level esp-idf README.
+Make sure that IDF_PATH environment variable is set to point to the path of esp-idf top-level directory.
+
+Change into tools/unit-test-app directory to configure and build it:
+
+* `make menuconfig` - configure unit test app.
+
+* `make TESTS_ALL=1` - build unit test app with tests for each component having tests in the ``test`` subdirectory.
+* `make TEST_COMPONENTS='xxx'` - build unit test app with tests for specific components. 
+
+When the build finishes, it will print instructions for flashing the chip. You can simply run ``make flash`` to flash all build output.
+
+You can also run ``make flash TESTS_ALL=1`` or ``make TEST_COMPONENTS='xxx'`` to build and flash. Everything needed will be rebuilt automatically before flashing. 
+
+Use menuconfig to set the serial port for flashing.
+
+Running unit tests
+------------------
+
+After flashing reset the ESP32 and it will boot the unit test app.
+
+Unit test app prints a test menu with all available tests.
+
+Test cases can be run by inputting one of the following:
+
+- Test case name in quotation marks to run a single test case 
+
+- Test case index to run a single test case
+
+- Module name in square brackets to run all test cases for a specific module
+
+- An asterisk to run all test cases