docs: add definition and minimum criteria for samples

Adding guidelines for writing samples which includes definition
and minimum criteria to qualify as a sample.

Signed-off-by: Aastha Grover <aastha.grover@intel.com>

samples/index.rst

@@ -8,6 +8,7 @@ Samples and Demos
    :maxdepth: 2
    :glob:
 
+   sample_definition_and_criteria
    classic
    basic/*
    userspace/*

samples/sample_definition_and_criteria.rst

@@ -0,0 +1,102 @@
+.. _definition_and_criteria:
+
+Sample Definition and Criteria
+##############################
+
+Definition
+==========
+
+A sample is a concise Zephyr application that provides an accessible overview of one or
+more features, subsystems, or modules. This includes kernel services, drivers, protocols, etc.
+Samples should be limited in scope and should focus only on demonstrating non-trivial or
+essential aspects of the subsystem(s) or module(s) being highlighted.
+
+Sample Criteria
+===============
+
+1. Samples must not be used as a testcase.
+++++++++++++++++++++++++++++++++++++++++++
+  * The primary purpose of a sample is to provide a reference to the user.
+  * Samples must not use Zephyr's testing framework.
+
+    * Must not use :kconfig:option:`CONFIG_ZTEST` or :kconfig:option:`CONFIG_ZTEST_NEW_API`.
+    * Must not use zasserts in samples.
+
+  * If a sample can provide output that can be verified, then output should be evaluated against
+    expected value to have some level of testing for the sample itself.
+    Refer to :zephyr_file:`doc/develop/test/twister.rst` for more details.
+  * Samples are optional.
+
+2. Twister should be able to build every sample.
+++++++++++++++++++++++++++++++++++++++++++++++++
+  * Every sample must have a YAML file. Reference: :zephyr_file:`doc/develop/test/twister.rst`.
+
+    **For example:**
+
+    .. code-block:: yaml
+
+      tests:
+        sample.kernel.cond_var:
+          integration_platforms:
+            - native_posix
+          tags: kernel condition_variables
+          harness: console
+          harness_config:
+            type: one_line
+            regex:
+              - ".*Waited and joined with 3 threads"
+
+  **Guidelines for Samples:**
+    * Minimize the use of ``platform_allow`` and architecture filters.
+    * Do not mark the test as build only unless necessary.
+    * Any test case-specific configuration options are added using ``extra_args`` or
+      ``extra_configs`` options in the YAML file. The `prj.conf` file should have the in-common
+      configuration options.
+    * The sample itself can be evaluated using multiple configurations in the sample's YAML file.
+      For example, the sample is used to run with different logging modes using multiple scenarios
+      in ``samples/subsys/logging/syst``.
+    * Sample output can be validated leveraging the ``harness_config`` regex option,
+      wherever applicable.
+
+3. Samples should target multiple platforms and architectures.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+  * Minimize the use of ``platform_allow`` and architecture filters as it limits the scope
+    of testing to the mentioned platforms and architectures.
+    Reference: :zephyr_file:`doc/develop/test/twister.rst`
+  * Make use of ``integration_platforms`` to limit the scope when there are timing or
+    resource constraints.
+  * Make the sample as generic as possible. Avoid making a sample platform specific unless it is
+    for particular hardware.
+
+4. A sample should provide sufficient coverage of a subsystem, feature, or module.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+  **DO's:**
+    * Cover the most common and important use cases of the functionality.
+    * Keep the code simple and easy to read. Example: :zephyr_file:`samples/philosophers`.
+
+  **DONT's:**
+    * Samples must not test the negative or edge case behaviors.
+    * Must not be unit tests.
+
+5. Samples must be documented.
+++++++++++++++++++++++++++++++
+  * Samples must have a ``README.rst`` file in the samples folder.
+    Example: ``samples/subsys/foo/README.rst``. clearly explaining the purpose of the sample, its
+    HW requirements, and the expected sample output, if applicable.
+  * Ensure that the ``README.rst`` file is accessible in the sample hierarchy starting at
+    ``samples/index.rst``.
+
+  **README Template:**
+    * Overview, if applicable.
+    * SW/HW requirements
+    * Building & Running instructions
+    * Sample output, if applicable.
+
+6. A sample should be a reference, not a tutorial.
+++++++++++++++++++++++++++++++++++++++++++++++++++
+  * Should have minimal comments, when applicable.
+  * Should concisely demonstrate HOW to solve a problem, not WHY.
+
+
+As a starting point, this sample is a good example to refer to
+:zephyr_file:`samples/kernel/condition_variables/condvar`.