Add tests for banner role

src/__tests__/role-helpers.js

@@ -16,6 +16,7 @@ afterEach(() => {
 
 function setup() {
   const {getByTestId} = render(`
+<header data-testid="a-header">Banner header</header>
 <section aria-label="a region" data-testid='named-section'>
   <a href="http://whatever.com" data-testid="a-link">link</a>
   <a>invalid link</a>
@@ -105,6 +106,7 @@ function setup() {
     textarea: getByTestId('a-textarea'),
     dt: getByTestId('a-dt'),
     dd: getByTestId('a-dd'),
+    header: getByTestId('a-header'),
   }
 }
 
@@ -139,6 +141,7 @@ test('getRoles returns expected roles for various dom nodes', () => {
     namedForm,
     dd,
     dt,
+    header,
   } = setup()
 
   expect(getRoles(namedSection)).toEqual({
@@ -161,6 +164,9 @@ test('getRoles returns expected roles for various dom nodes', () => {
     term: [dt],
     definition: [dd],
   })
+  expect(getRoles(header)).toEqual({
+    banner: [header],
+  })
 })
 
 test('logRoles calls console.log with output from prettyRoles', () => {