Fix failing test

src/core/components/layout-utils.jsx

@@ -183,7 +183,7 @@ export class Select extends React.Component {
         { allowEmptyValue ? <option value="">--</option> : null }
         {
           allowedValues.map(function (item, key) {
-            return <option key={ key } value={ String(item) }>{ item }</option>
+            return <option key={ key } value={ String(item) }>{ String(item) }</option>
           })
         }
       </select>

src/core/json-schema-components.js

@@ -189,8 +189,8 @@ export class JsonSchema_boolean extends Component {
     return (<Select className={ errors.length ? "invalid" : ""}
                     title={ errors.length ? errors  : ""}
                     value={ String(value) }
-                    allowedValues={ fromJS(["true", "false"]) }
-                    allowEmptyValue={ true }
+                    allowedValues={ fromJS(schema.enum || ["true", "false"]) }
+                    allowEmptyValue={ !this.props.required }
                     onChange={ this.onEnumChange }/>)
   }
 }