Improve CLI error reporting

spec/producer/core/cli_spec.rb

@@ -44,7 +44,7 @@ module Producer::Core
         end
       end
 
-      context 'when a runtime error is raised' do
+      context 'when an error is raised' do
         let(:recipe_file) { fixture_path_for 'recipes/raise.rb' }
 
         it 'exits with a return status of 70' do
@@ -52,9 +52,9 @@ module Producer::Core
             .to raise_error(SystemExit) { |e| expect(e.status).to eq 70 }
         end
 
-        it 'prints exception name and message and the error stream' do
+        it 'prints a report to the error stream' do
           expect { trap_exit { run! } }
-            .to output("RemoteCommandExecutionError: false\n").to_stderr
+            .to output(/\ARemoteCommandExecutionError: false$/).to_stderr
         end
       end
     end

spec/producer/core/error_formatter_spec.rb

@@ -0,0 +1,50 @@
+require 'spec_helper'
+
+module Producer
+  module Core
+    describe ErrorFormatter do
+      let(:debug)         { false }
+      let(:force_cause)   { [] }
+      let(:options)       { { debug: debug, force_cause: force_cause } }
+      subject(:formatter) { described_class.new(options) }
+
+      describe '#debug?' do
+        it 'returns false' do
+          expect(formatter.debug?).to be false
+        end
+
+        context 'when debug is enabled' do
+          let(:debug) { true }
+
+          it 'returns true' do
+            expect(formatter.debug?).to be true
+          end
+        end
+      end
+
+      describe '#format' do
+        let(:message)   { 'some exception' }
+        let(:exception) { Exception.new(message) }
+
+        before { exception.set_backtrace %w[back trace] }
+
+        it 'formats the message' do
+          expect(formatter.format exception)
+            .to match /^Exception: some exception$/
+        end
+
+        it 'indents the backtrace' do
+          expect(formatter.format exception).to match /^\s+back$/
+        end
+
+        context 'filtering' do
+          before { exception.set_backtrace %w[back trace /producer-core/lib/] }
+
+          it 'excludes producer code from the backtrace' do
+            expect(formatter.format exception).not_to include 'producer-core'
+          end
+        end
+      end
+    end
+  end
+end