contributor-guide: add notes for tests

This adds some hints that and how changes should be tested when contributing.

Fixes [YOCTO #15412]

(From yocto-docs rev: 649843f4d20d1d840e1c6c4ce15e89b3a8508e0f)

Signed-off-by: Simone Weiß <simone.p.weiss@posteo.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/contributor-guide/submit-changes.rst

@@ -221,6 +221,38 @@ to add the upgraded version.
    <https://www.kernel.org/doc/html/latest/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes>`__
    in the Linux kernel documentation.
 
+Test your changes
+-----------------
+
+For each contributions you make, you should test your changes as well.
+For this the Yocto Project offers several types of tests. Those tests cover
+different areas and it depends on your changes which are feasible. For example run:
+
+   -  For changes that affect the build environment:
+
+      -  ``bitbake-selftest``: for changes within BitBake
+
+      -  ``oe-selftest``: to test combinations of BitBake runs
+
+      -  ``oe-build-perf-test``: to test the performance of common build scenarios
+
+   -  For changes in a recipe:
+
+      - ``ptest``: run package specific tests, if they exist
+
+      - ``testimage``: build an image, boot it and run testcases on it
+
+      - If applicable, ensure also the ``native`` and ``nativesdk`` variants builds
+
+   -  For changes relating to the SDK:
+
+      - ``testsdk``: to build, install and run tests against a SDK
+
+      - ``testsdk_ext``: to build, install and run tests against an extended SDK
+
+Note that this list just gives suggestions and is not exhaustive. More details can
+be found here: :ref:`test-manual/intro:Yocto Project Tests --- Types of Testing Overview`.
+
 Creating Patches
 ================