Update testing information for Bazel and Bazelisk

TESTING.md

@@ -1,5 +1,7 @@
 # Testing
-The preferred mechanism for testing is using the [Bazel](https://bazel.build/) build system. This uses files called `BUILD` ([example](https://github.com/google/open-location-code/blob/main/python/BUILD) to provide rules to build code and run tests).
+The preferred mechanism for testing is using the [Bazel](https://bazel.build/) build system.
+This uses files called `BUILD` ([example](https://github.com/google/open-location-code/blob/main/python/BUILD) to provide rules to build code and run tests).
+Rather than installing Bazel directly, install [Bazelisk](https://github.com/bazelbuild/bazelisk), a launcher for Bazel that allows configuration of the specific version to use.
 
 Create a `BUILD` file in your code directory with a [test rule](https://bazel.build/versions/master/docs/test-encyclopedia.html).
 You can then test your code by running:
@@ -15,7 +17,8 @@ bazel test ...:all
 ```
 
 ## Automated Integration Testing
-On pushes and pull requests changes are tested via GitHub Actions. You can see the current test status in the [Actions tab](https://github.com/google/open-location-code/actions/workflows/main.yml?query=branch%3Amain).
+On pushes and pull requests changes are tested via GitHub Actions.
+You can see the current test status in the [Actions tab](https://github.com/google/open-location-code/actions/workflows/main.yml?query=branch%3Amain).
 
 The testing configuration is controlled by the [`.github/workflows/main.yml`](.github/workflows/main.yml) file.
 
@@ -65,8 +68,17 @@ An example of a language using bazel is Python:
         run: bazel test --test_output=all ${OLC_PATH}:all
 ```
 
-Bazel is pre-installed on GitHub-hosted runners which are used to run CI, so there's no need to install it. This example also shows how to test with multiple versions of a language.
+Bazel is pre-installed on GitHub-hosted runners which are used to run CI, so there's no need to install it.
+This example also shows how to test with multiple versions of a language.
 
 ### Adding Your Tests
 
-Simply add a new section to the `.github/workflows/main.yml` file with the appropriate language, and either the native test command or call `bazel test` like the other examples. More information about GitHub actions can be found in the [documentation](https://docs.github.com/en/actions/quickstart).
+Simply add a new section to the `.github/workflows/main.yml` file with the appropriate language, and either the native test command or call `bazel test` like the other examples.
+More information about GitHub actions can be found in the [documentation](https://docs.github.com/en/actions/quickstart).
+
+## Bazel version
+
+Currently (2004), Bazel version 8 or later cannot be used for testing. (See issue #662.)
+The `js/closure` tests require using https://github.com/bazelbuild/rules_closure, which is not yet available as a Bazel module.
+That dependency must be specified using a Bazel `WORKSPACE` file, and the version of Bazel to use is specified in the `.bazeliskrc` file.
+