Updated the unit test documentation to reflect the transition to PW. (#33492)

* Revised unit testing documentation to refer to PW tests.

* Documentation update

* More doc updates

* More doc updates

* More doc updates

* More doc updates

* More doc updates

* More doc updates

* Updated documentation to reflect PW

* Fixed spelling error

* Replaced gtest.h include.

* Modified MessagingContext and its subclasses as well as AppContext to reflect PW migration.

* Undid last commit.

* Undid last commit.

* Undid last commit.

* Restyled by prettier-markdown

* Changed the includes to be consistent.

* Cleaned up example code comments

---------

Co-authored-by: Restyled.io <commits@restyled.io>

Author: feasel0

docs/guides/openiotsdk_unit_tests.md

@@ -6,8 +6,8 @@ tests that are located in the `test` directory, e.g. `src/inet/tests`. Those
 sources are built as a static library that can be linked to the unit test
 application separately or as a monolithic test library. The common Matter test
 library collects all test cases and provides the engine based on
-[Nest Labs Unit Test](https://github.com/nestlabs/nlunit-test) to run them in
-the application.
+[Pigweed Unit Test](https://pigweed.dev/pw_unit_test) to run them in the
+application.
 
 The Open IoT SDK unit tests implementation are located in the
 `src/test_driver/openiotsdk/unit-tests` directory. This project builds a
@@ -27,6 +27,7 @@ ChipCryptoTests
 CoreTests
 CredentialsTest
 DataModelTests
+ICDServerTests
 InetLayerTests
 MdnsTests
 MessagingLayerTests
@@ -41,7 +42,6 @@ SetupPayloadTests
 SupportTests
 SystemLayerTests
 TestShell
-TransportLayerTests
 UserDirectedCommissioningTests
 ```