docs: clarify meaning of ellipsis in bazel command (#43890)

PR Close #43890

docs/DEVELOPER.md

@@ -81,6 +81,12 @@ of for all packages. Read more about this in the [BAZEL.md](./BAZEL.md) document
 You should execute all test suites before submitting a PR to GitHub.
 - `yarn test //packages/...`
 
+**Note**: The ellipsis in the commands above is not meant to be substituted by a package name, but
+is used by Bazel as a wildcard to execute all tests in the specified path. To execute tests for a
+single package, the commands are (exemplary):
+- `yarn test //packages/core/...` for all tests, or
+- `yarn test //packages/core/test:test_web_firefox` for a particular test suite.
+
 **Note**: The first test run will be much slower than future runs. This is because future runs will
 benefit from Bazel's capability to do incremental builds.