(maint) Introduce BEAKER_HYPERVISOR

Beaker already knows how to generate hosts on the fly using
beaker-hostgenrator. The problem is that there's no way to choose the
default hypervisor. This means you always specify the long form. Using
an environment variable we can simplify configs.

CHANGELOG.md

@@ -15,6 +15,7 @@ git logs & PR history.
 
 ### Added
 - `--preserve-state` flag will preserve a given host options hash across subcommand runs(BKR-1541)
+- `BEAKER_HYPERVISOR` environment variable to choose the beaker-hostgenerator hypervisor
 
 ### Changed
 

docs/tutorials/lets_write_a_test.md

@@ -26,6 +26,26 @@ What needs to happen in this test:
 
 This command will generate a host file for our system under test (SUT). It will use vmpooler as hypervisor for the host. Please check out [this](https://github.com/puppetlabs/beaker/tree/master/docs/how_to/hypervisors) doc to learn more about hypervisors for beaker.
 
+## Creating the host configuration on at runtime
+
+When you don't want to store a static file, you can also let [beaker-hostgenerator](https://github.com/puppetlabs/beaker-hostgenerator) generate it on the fly. The filename is used as a host specification which comes down to the environment variable `BEAKER_setfile`. A simple example is:
+
+```
+BEAKER_setfile=centos7-64
+```
+
+It's also possible to set the hypervisor and hostname:
+
+```
+BEAKER_setfile=centos7-64{hypervisor=docker\,hostname=centos7-64.example.com}
+```
+
+An alternative way to set the hypervisor is `BEAKER_HYPERVISOR`:
+
+```
+BEAKER_setfile=centos7-64 BEAKER_HYPERVISOR=docker
+```
+
 ## Install and run HTTPD
 
 Make a file named `install.rb` and put the following code into it:

lib/beaker/options/parser.rb

@@ -291,8 +291,11 @@ def parse_hosts_options
         $stdout.puts dne_message
         require 'beaker-hostgenerator'
 
+        host_generator_options = [ @options[:hosts_file] ]
+        host_generator_options += [ '--hypervisor', ENV['BEAKER_HYPERVISOR'] ] if ENV['BEAKER_HYPERVISOR']
+
         hosts_file_content = begin
-          bhg_cli = BeakerHostGenerator::CLI.new( [ @options[:hosts_file] ] )
+          bhg_cli = BeakerHostGenerator::CLI.new(host_generator_options)
           bhg_cli.execute
         rescue BeakerHostGenerator::Exceptions::Error,
           BeakerHostGenerator::Exceptions::InvalidNodeSpecError => error

spec/beaker/options/parser_spec.rb

@@ -376,13 +376,46 @@ def mock_out_parsing
             ).and_return( cli_execute_return )
             expect( BeakerHostGenerator::CLI ).to receive(
               :new
+            ).with(
+              [ 'notafile.yml' ]
             ).and_return( mock_beaker_hostgenerator_cli )
             allow( Beaker::Options::HostsFileParser ).to receive(
               :parse_hosts_string
             ).with( cli_execute_return )
             parser.parse_hosts_options
           end
 
+          it 'calls beaker-hostgenerator to get hosts information with a default hypervisor' do
+            old_beaker_hypervisor = ENV['BEAKER_HYPERVISOR']
+            begin
+              ENV['BEAKER_HYPERVISOR'] = 'docker'
+
+              parser.instance_variable_set( :@options, {
+                :hosts_file => 'notafile.yml'
+              } )
+              allow( Beaker::Options::HostsFileParser ).to receive(
+                :parse_hosts_file
+              ).and_raise( Errno::ENOENT )
+
+              mock_beaker_hostgenerator_cli = Object.new
+              cli_execute_return = 'job150865'
+              expect( mock_beaker_hostgenerator_cli ).to receive(
+                :execute
+              ).and_return( cli_execute_return )
+              expect( BeakerHostGenerator::CLI ).to receive(
+                :new
+              ).with(
+                [ 'notafile.yml', '--hypervisor', 'docker' ]
+              ).and_return( mock_beaker_hostgenerator_cli )
+              allow( Beaker::Options::HostsFileParser ).to receive(
+                :parse_hosts_string
+              ).with( cli_execute_return )
+              parser.parse_hosts_options
+            ensure
+              ENV['BEAKER_HYPERVISOR'] = old_beaker_hypervisor
+            end
+          end
+
           it 'sets the :hosts_file_generated flag to signal others when needed' do
             options_test = {
               :hosts_file => 'not_a_file.yml'