doc: release notes: add comment about tests

Adding a note about new tests and expanded
test case list for 2.0.0 release notes.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

doc/releases/release-notes-2.0.rst

@@ -462,7 +462,8 @@ Documentation
 Tests and Samples
 *****************
 
-* TBD
+* We have implemented additional tests and significantly expanded the
+  amount of test cases in existing tests to increase code coverage.
 
 Issue Related Items
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