feat: allow specification of puppet version

Author: jordanbreen28

README.md

@@ -29,6 +29,15 @@ Install Litmus as a gem by running `gem install puppet_litmus`.
 
 - Note if you choose to override the `litmus_inventory.yaml` location, please ensure that the directory structure you define exists.
 
+## Install a specific puppet agent version
+
+To install a specific version of the puppet agent, you can export the `PUPPET_VERSION` env var, like below:
+```
+export PUPPET_VERSION=8.8.1
+```
+
+When set, the `litmus:install_agent` rake task will install the specified version. The default is `latest`.
+
 ## matrix_from_metadata_v3
 
 matrix_from_metadata_v3 tool generates a github action matrix from the supported operating systems listed in the module's metadata.json.

lib/puppet_litmus/rake_helper.rb

@@ -129,11 +129,11 @@ def tear_down(node_name, inventory_hash)
 
   def install_agent(collection, targets, inventory_hash)
     include ::BoltSpec::Run
-    params = if collection.nil?
-               {}
-             else
-               { 'collection' => collection }
-             end
+    puppet_version = ENV.fetch('PUPPET_VERSION', nil)
+    params = {}
+    params['collection'] = collection  if collection
+    params['version'] = puppet_version if puppet_version
+
     raise "puppet_agent was not found in #{DEFAULT_CONFIG_DATA['modulepath']}, please amend the .fixtures.yml file" \
       unless File.directory?(File.join(DEFAULT_CONFIG_DATA['modulepath'], 'puppet_agent'))