doc: add test case docstring example to dts rst

Add a section to the dts rst under How to Write a Test Suite
which provides an example for how to write a test case
docstring, including a steps and verify section.

Signed-off-by: Dean Marx <[email protected]>
Reviewed-by: Luca Vizzarro <[email protected]>

Author: dmarxIOL

doc/guides/tools/dts.rst

@@ -427,6 +427,22 @@ and performance test cases should use ``@perf_test``.
 A test suite may include any number of functional and/or performance test cases.
 Each suite should focus on testing a single feature (one feature = one test suite).
 
+   Test case docstrings must include a Steps and Verify section. For example:
+
+   Example::
+
+      @func_test
+      def test_basic_link(self):
+      """Tests basic link status.
+
+         Steps:
+            * Launch testpmd.
+            * Check port info.
+
+         Verify:
+            * Port info shows link status is up.
+      """
+
 Setup and Teardown Hooks
 ~~~~~~~~~~~~~~~~~~~~~~~~