Update tests.mdx

docs/contributors/tests.mdx

@@ -61,10 +61,22 @@ Examples:
 
 A level 5 heading (`#####`), with the text being one of the following:
 
-- `##### only` -- If at least one test has the `only` annotation, the runner will run this/these test(s).
 - `##### skip` -- If a test has the `skip` annotation, the runner will not run that test.
 
-These are typically added to tests temporarily, so try not to commit tests with annotations. There must be either zero or one annotations in a test.
+There must be either zero or one such annotation in a test.
+
+This annotation comes handy in situation where one might need to skip the execution of some written tests temporarily due to various reasons like : 
+- Some functionalities which are supposed to be tested might not be implemented yet, OR
+- There might be some bugs related to it.
+
+Note: `##### only` which is used to run single test has been removed in the favour of cargo option.
+
+To run a single test locally one can use [cargo option](https://doc.rust-lang.org/rustc/tests/index.html#--test) "--test".
+
+Example usage of cargo option:
+````sh
+cargo test --test execution_spec -- --test "test_filter"
+````
 
 ### Blocks