Simplify specs for stderr handling

Instead of setting up or using a shell script, just use Ruby with a
script on the command line.

spec/aruba/matchers/command_spec.rb

@@ -71,20 +71,7 @@ def announcer(*args)
     end
 
     context 'when have output hello world on stderr' do
-      before :each do
-        string = <<-EOS.strip_heredoc
-        #!/usr/bin/env bash
-
-        echo $* >&2
-        EOS
-
-        File.open(expand_path('cmd.sh'), 'w') { |f| f.puts string }
-
-        File.chmod 0o755, expand_path('cmd.sh')
-        prepend_environment_variable 'PATH', "#{expand_path('.')}#{File::PATH_SEPARATOR}"
-      end
-
-      let(:cmd) { "cmd.sh #{output}" }
+      let(:cmd) { "ruby -e 'warn \"#{output}\"'" }
 
       before(:each) { run_command(cmd) }
 
@@ -108,20 +95,7 @@ def announcer(*args)
     end
 
     context 'when have output hello world on stderr' do
-      before :each do
-        string = <<-EOS.strip_heredoc
-        #!/usr/bin/env bash
-
-        echo $* >&2
-        EOS
-
-        File.open(expand_path('cmd.sh'), 'w') { |f| f.puts string }
-
-        File.chmod 0o755, expand_path('cmd.sh')
-        prepend_environment_variable 'PATH', "#{expand_path('.')}#{File::PATH_SEPARATOR}"
-      end
-
-      let(:cmd) { "cmd.sh #{output}" }
+      let(:cmd) { "ruby -e 'warn \"#{output}\"'" }
 
       before(:each) { run_command(cmd) }
 
@@ -145,20 +119,7 @@ def announcer(*args)
     end
 
     context 'when have output hello world on stderr' do
-      before :each do
-        string = <<-EOS.strip_heredoc
-        #!/usr/bin/env bash
-
-        echo $* >&2
-        EOS
-
-        File.open(expand_path('cmd.sh'), 'w') { |f| f.puts string }
-
-        File.chmod 0o755, expand_path('cmd.sh')
-        prepend_environment_variable 'PATH', "#{expand_path('.')}#{File::PATH_SEPARATOR}"
-      end
-
-      let(:cmd) { "cmd.sh #{output}" }
+      let(:cmd) { "ruby -e 'warn \"#{output}\"'" }
 
       before(:each) { run_command(cmd) }
 

spec/aruba/processes/spawn_process_spec.rb

@@ -22,7 +22,7 @@
   end
 
   describe "#stderr" do
-    let(:command) { 'fixtures/spawn_process/stderr.sh yo' }
+    let(:command) { "ruby -e 'warn \"yo\"'" }
 
     before(:each) { process.start }
     before(:each) { process.stop }