diff --git a/lib/completely/commands/test.rb b/lib/completely/commands/test.rb
index 9493317..ebdd006 100644
--- a/lib/completely/commands/test.rb
+++ b/lib/completely/commands/test.rb
@@ -22,10 +22,13 @@ class Test < Base
 
       def run
         puts tester.test(compline).join "\n"
-        return unless args['--keep']
 
-        File.write 'completely-tester.sh', tester_script
-        puts 'saved completely-tester.sh'
+        if args['--keep']
+          File.write 'completely-tester.sh', tester_script
+          puts 'saved completely-tester.sh'
+        end
+
+        syntax_warning unless completions.valid?
       end
 
     private
diff --git a/spec/completely/commands/test_spec.rb b/spec/completely/commands/test_spec.rb
index 672bea7..87f82a0 100644
--- a/spec/completely/commands/test_spec.rb
+++ b/spec/completely/commands/test_spec.rb
@@ -65,4 +65,16 @@
         .to raise_approval('cli/test/error')
     end
   end
+
+  context 'with an invalid configuration' do
+    before do
+      reset_tmp_dir
+      File.write 'spec/tmp/in.yaml', { 'one' => %w[anything], 'two' => %w[something] }.to_yaml
+      ENV['COMPLETELY_CONFIG_PATH'] = 'spec/tmp/in.yaml'
+    end
+
+    it 'outputs a warning to STDERR' do
+      expect { subject.execute %w[test on] }.to output_approval('cli/warning').to_stderr
+    end
+  end
 end