Ensure render function does not have undefined object

CHANGELOG.md

@@ -24,6 +24,8 @@ Internal:
 
 - Update pre-release step to check for new components
 (PR [#574](https://github.com/alphagov/govuk-frontend/pull/574))
+- Ensure render function does not have undefined object
+  (PR [#587](https://github.com/alphagov/govuk-frontend/pull/587))
 
 ## 0.0.25-alpha (Breaking release)
 

lib/jest-helpers.js

@@ -20,6 +20,9 @@ nunjucks.configure(configPaths.src, {
  * @returns {function} returns cheerio (jQuery) instance of the template for easy DOM querying
  */
 function render (componentName, params) {
+  if (typeof params === 'undefined') {
+    throw new Error('Parameters passed to `render` should be an object but are undefined')
+  }
   const output = nunjucks.render(componentName + '/template.njk', { params })
   return cheerio.load(output)
 }

src/button/template.test.js

@@ -241,7 +241,7 @@ describe('Button', () => {
     })
 
     it('renders an input[type=submit] if you don\'t pass anything', () => {
-      const $ = render('button')
+      const $ = render('button', {})
 
       const $component = $('.govuk-c-button')
       expect($component.get(0).tagName).toEqual('input')

src/input/template.test.js

@@ -43,7 +43,7 @@ describe('Input', () => {
     })
 
     it('renders with type="text" by default', () => {
-      const $ = render('input')
+      const $ = render('input', {})
 
       const $component = $('.govuk-c-input')
       expect($component.attr('type')).toEqual('text')