Convert the tests from test components to component-specific test apps (IEC-11)

[igrr]

Combining multiple test components into a single app doesn't scale well. For example, we already can't build the test_app for esp32s2, since the app doesn't fit into RAM. For this and other similar reasons, we have mostly migrated from test components to the component-specific test apps in IDF.

The task is to investigate how to do this in idf-extra-components, make the required changes to the tests and the CI workflow.

• Use https://github.com/espressif/idf-build-apps to create the build matrix and perform the builds. — already done for the examples build
• Convert the test_app into separate component test apps
• Only build and test the components which have changed in the PR, and components which had changes to their dependencies.
• Build and test the examples inside components as well. (A test app is very similar to an example, it just doesn't get uploaded to the registry along with the component.) — already done

Potential problems:

• Converting from test components to test apps: until IDF v5.0, we didn't have the WHOLE_ARCHIVE feature in the build system, which makes creating test apps a bit harder. We could work around this by using the -u some_symbol trick, to force linking all the test object files. — IDF v4.4 is EOL, so this is not an issue anymore.

[lijunru-hub]

In CMake, I can't find the -U option. How can I achieve the functionality of WHOLE_ARCHIVE in IDF 4.4? Could you provide a CMake template for this?

[igrr]

@lijunru-hub In v4.4 you can do it as done here and here. Note that you need one such hook symbol per object file.

[igrr]

This is probably becoming more relevant, as the number of components in the repo has increased and we do a lot of unnecessary builds/tests when only one of the components gets updated.