Add a unit test to illustrate the pyvenv bootstrap issue

This module that manage python needs python to be installed in order to
work properly under certain conditions.

When python is not installed on a node, the python_version fact does not
have a value.  When using `python::pyvenv` on such a system without a
specific version set, a call of the split() function on this unde value
cause an error te be raised:

```
   Error: Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error: Error while evaluating a Function Call, The function 'split' was called with arguments it does not accept. It expects one of:
    (String str, String pattern)
      rejected: parameter 'str' expects a String value, got Undef
    (String str, Regexp pattern)
      rejected: parameter 'str' expects a String value, got Undef
    (String str, Type[Regexp] pattern)
      rejected: parameter 'str' expects a String value, got Undef
    (Sensitive[String] sensitive, String pattern)
      rejected: parameter 'sensitive' expects a Sensitive[String] value, got Undef
    (Sensitive[String] sensitive, Regexp pattern)
      rejected: parameter 'sensitive' expects a Sensitive[String] value, got Undef
    (Sensitive[String] sensitive, Type[Regexp] pattern)
      rejected: parameter 'sensitive' expects a Sensitive[String] value, got Undef (file: /etc/puppetlabs/code/environments/production/modules/python/manifests/pyvenv.pp, line: 48, column: 34) (file: /etc/puppetlabs/code/environments/production/modules/taiga/manifests/back/install.pp, line: 15) on node debian12-64-puppet7.example.com
```

Author: smortex

spec/defines/pyvenv_spec.rb

@@ -6,83 +6,93 @@
   on_supported_os.each do |os, facts|
     next if os == 'gentoo-3-x86_64'
 
+    let :title do
+      '/opt/env'
+    end
+
     context "on #{os}" do
-      let :facts do
-        # python3 is required to use pyvenv
-        facts.merge(
-          python3_version: '3.5.1'
-        )
-      end
-      let :title do
-        '/opt/env'
+      context "with default parameters" do
+        let :facts do
+          facts
+        end
+
+        it { is_expected.to compile }
       end
 
-      context 'with default parameters' do
-        it { is_expected.to contain_file('/opt/env').that_requires('Class[python::install]') }
-        it { is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('pyvenv-3.5 --clear   /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools') }
+      context "with a specific python3 version" do
+        let :facts do
+          # python3 is required to use pyvenv
+          facts.merge(
+            python3_version: '3.5.1'
+          )
+        end
+        context 'with default parameters' do
+          it { is_expected.to contain_file('/opt/env').that_requires('Class[python::install]') }
+          it { is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('pyvenv-3.5 --clear   /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools') }
+        end
+
+        describe 'when ensure' do
+          context 'is absent' do
+            let :params do
+              {
+                ensure: 'absent'
+              }
+            end
+
+            it {
+              expect(subject).to contain_file('/opt/env').with_ensure('absent').with_purge(true)
+            }
+          end
+        end
       end
 
-      describe 'when ensure' do
-        context 'is absent' do
+      context "prompt on #{os} with python 3.6" do
+        let :facts do
+          # python 3.6 is required for venv and prompt
+          facts.merge(
+            python3_version: '3.6.1'
+          )
+        end
+        let :title do
+          '/opt/env'
+        end
+
+        context 'with prompt' do
           let :params do
             {
-              ensure: 'absent'
+              prompt: 'custom prompt',
             }
           end
 
           it {
-            expect(subject).to contain_file('/opt/env').with_ensure('absent').with_purge(true)
+            is_expected.to contain_file('/opt/env').that_requires('Class[python::install]')
+            is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('python3.6 -m venv --clear  --prompt custom\\ prompt /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools')
           }
         end
       end
-    end
-
-    context "prompt on #{os} with python 3.6" do
-      let :facts do
-        # python 3.6 is required for venv and prompt
-        facts.merge(
-          python3_version: '3.6.1'
-        )
-      end
-      let :title do
-        '/opt/env'
-      end
 
-      context 'with prompt' do
-        let :params do
-          {
-            prompt: 'custom prompt',
-          }
+      context "prompt on #{os} with python 3.5" do
+        let :facts do
+          facts.merge(
+            python3_version: '3.5.1'
+          )
+        end
+        let :title do
+          '/opt/env'
         end
 
-        it {
-          is_expected.to contain_file('/opt/env').that_requires('Class[python::install]')
-          is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('python3.6 -m venv --clear  --prompt custom\\ prompt /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools')
-        }
-      end
-    end
-
-    context "prompt on #{os} with python 3.5" do
-      let :facts do
-        facts.merge(
-          python3_version: '3.5.1'
-        )
-      end
-      let :title do
-        '/opt/env'
-      end
+        context 'with prompt' do
+          let :params do
+            {
+              prompt: 'custom prompt',
+            }
+          end
 
-      context 'with prompt' do
-        let :params do
-          {
-            prompt: 'custom prompt',
+          it {
+            is_expected.to contain_file('/opt/env').that_requires('Class[python::install]')
+            is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('pyvenv-3.5 --clear   /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools')
           }
         end
-
-        it {
-          is_expected.to contain_file('/opt/env').that_requires('Class[python::install]')
-          is_expected.to contain_exec('python_virtualenv_/opt/env').with_command('pyvenv-3.5 --clear   /opt/env && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade pip && /opt/env/bin/pip --log /opt/env/pip.log install --upgrade setuptools')
-        }
       end
     end
   end