doc: add example to test doc for clarity

Update the documentation for test execution for tests in a single file

PR-URL: #27561
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

BUILDING.md

@@ -295,10 +295,11 @@ If you want to run the linter without running tests, use
 `make lint`/`vcbuild lint`. It will run both JavaScript linting and
 C++ linting.
 
-If you are updating tests and just want to run a single test to check it:
+If you are updating tests and want to run tests in a single test file
+(e.g. `test/parallel/test-stream2-transform.js`):
 
 ```text
-$ python tools/test.py -J --mode=release parallel/test-stream2-transform
+$ python tools/test.py parallel/test-stream2-transform.js
 ```
 
 You can execute the entire suite of tests for a given subsystem