updated unit test related terms

doc/source/ch06_unittest.rst

@@ -36,7 +36,7 @@ To run unit tests collected from directory ``.``, and calculate coverage for sou
 
 You will see messages like below
 
-.. code-block:: plain
+.. code-block:: none
 
     ============================ test session starts ============================
     platform darwin -- Python 3.9.7, pytest-7.1.3, pluggy-0.13.1

doc/source/ch09_build.rst

@@ -67,7 +67,7 @@ The build log includes 6 sections.
 An example of test summary is at the end of build log (the attached ``build.zip``).
 If all checks/tests/validations passed, you will see a section as below.
 
-.. code-block:: plain
+.. code-block:: none
 
     ===================== TEST SUMMARY =====================
     Test passed!
@@ -85,7 +85,7 @@ Unit test coverage report
 The ``build log`` also contains a section of unit test coverage report.
 An example is below.
 
-.. code-block:: plain
+.. code-block:: none
 
     ---------- coverage: platform darwin, python 3.9.7-final-0 -----------
     Name                                Stmts   Miss  Cover   Missing