(FM-7795) Cleanup java tests (#350)

* Add idempotent_apply function

* Remove unsupported OS specific code

* Remove outdated comments

* Improve unit test coverage

* Fix typo

spec/unit/facter/java_default_home_spec.rb

@@ -47,7 +47,7 @@ describe 'java_default_home' do
   context 'when java not present, return nil' do
     it do
       allow(Facter::Util::Resolution).to receive(:exec) # Catch all other calls
-      expect(Facter::Util::Resolution).to receive(:which).with('java').at_least(1).and_return(false)
+      expect(Facter::Util::Resolution).to receive(:which).with('java').at_least(1).and_return(nil)
       expect(Facter.value(:java_default_home)).to be_nil
     end
   end

spec/unit/facter/java_libjvm_path_spec.rb

@@ -1,17 +1,25 @@
 require 'spec_helper'
 
 describe 'java_libjvm_path' do
+  let(:java_default_home) { '/usr/lib/jvm/java-8-openjdk-amd64' }
+
   before(:each) do
     Facter.clear
     allow(Facter.fact(:kernel)).to receive(:value).once.and_return('Linux')
-    java_default_home = '/usr/lib/jvm/java-8-openjdk-amd64'
     allow(Facter.fact(:java_default_home)).to receive(:value).once.and_return(java_default_home)
-    allow(Dir).to receive(:glob).with("#{java_default_home}/jre/lib/**/libjvm.so").and_return(['/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server/libjvm.so'])
   end
 
-  context 'when on Linux, return libjvm path' do
+  context 'when libjvm exists' do
     it do
+      allow(Dir).to receive(:glob).with("#{java_default_home}/jre/lib/**/libjvm.so").and_return(['/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server/libjvm.so'])
       expect(Facter.value(:java_libjvm_path)).to eql '/usr/lib/jvm/java-8-openjdk-amd64/jre/lib/amd64/server'
     end
   end
+
+  context 'when libjvm does not exist' do
+    it do
+      allow(Dir).to receive(:glob).with("#{java_default_home}/jre/lib/**/libjvm.so").and_return([])
+      expect(Facter.value(:java_libjvm_path)).to be nil
+    end
+  end
 end