Make asdf plugin test determine plugin version with asdf latest

Fixes #541

CHANGELOG.md

@@ -4,6 +4,11 @@
 
 Features
 
+* Make `asdf plugin test` use the new `asdf latest` command. (#541)
+
+   If a plugin version is not given explicitly, we use `asdf latest` to
+   obtain the version of plugin to install for testing.
+
 * `asdf --version` displays git revision when asdf_dir is a git clone.
 
    This will allow better bug reports since people can now include the

lib/commands/plugin-test.sh

@@ -101,7 +101,7 @@ plugin_test_command() {
         if [ -n "$tool_version" ]; then
           version="$tool_version"
         else
-          version=${versions[${#versions[@]} - 1]}
+          version="$(asdf latest "$plugin_name")"
         fi
 
         if ! (asdf install "$plugin_name" "$version"); then