add support for testing scenarios where commands fail

spec/helpers/cib_object.rb

@@ -10,7 +10,7 @@ module Chef::RSpec
     module CIBObject
       # Return a Mixlib::ShellOut double which mimics successful
       # execution of a command, returning the given string on STDOUT.
-      def shellout_double(string)
+      def succeeding_shellout_double(string)
         shellout = double(Mixlib::ShellOut)
         shellout.stub(:environment).and_return({})
         shellout.stub(:run_command)
@@ -19,10 +19,38 @@ module Chef::RSpec
         shellout
       end
 
+      # Return a Mixlib::ShellOut double which mimics failed
+      # execution of a command, raising an exception when #error! is
+      # called.  We expect #error! to be called, because if it isn't,
+      # that probably indicates the code isn't robust enough.  This
+      # may need to be relaxed in the future.
+      def failing_shellout_double(stdout='', stderr='', exitstatus=1)
+        shellout = double(Mixlib::ShellOut)
+        shellout.stub(:environment).and_return({})
+        shellout.stub(:run_command)
+        shellout.stub(:stdout).and_return(stdout)
+        shellout.stub(:stderr).and_return(stderr)
+        shellout.stub(:exitstatus).and_return(exitstatus)
+        exception = Mixlib::ShellOut::ShellCommandFailed.new(
+          "Expected process to exit with 0, " +
+          "but received '#{exitstatus}'"
+        )
+        expect(shellout).to receive(:error!).and_raise(exception)
+        shellout
+      end
+
       # This stubs Mixlib::ShellOut.new with a sequence of doubles
-      # whose #stdout methods return a corresponding sequence of strings.
+      # with a corresponding sequence of behaviours.  This allows us
-      # This allows us to simulate the output of a series of shell
+      # to simulate the output of a series of shell commands being run
-      # commands being run via Mixlib::ShellOut.
+      # via Mixlib::ShellOut.  Each double either mimics a successful
+      # command execution whose #stdout method returns the given
+      # string, or a failed execution with the given exit code and
+      # STDOUT/STDERR.
+      #
+      # results is an Array describing the sequence of behaviours;
+      # each element is either a string mimicking STDOUT from
+      # successful command execution, or a [stdout, stderr, exitcode]
+      # status mimicking command execution failure.
       #
       # For example, "crm configure show" is executed by
       # #load_current_resource, and again later on for the :create
@@ -32,8 +60,12 @@ module Chef::RSpec
       # definition if we wanted to test modification of an existing
       # one.  If the test needs subsequent doubles to return different
       # values then stdout_strings can have more than one element.
-      def stub_shellout(*stdout_strings)
+      def stub_shellout(*results)
-        doubles = stdout_strings.map { |string| shellout_double(string) }
+        doubles = results.map { |result|
+          result.is_a?(String) ?
+              succeeding_shellout_double(result)
+            : failing_shellout_double(*result)
+        }
         Mixlib::ShellOut.stub(:new).and_return(*doubles)
       end
     end