Add test verifiying PageHeader dev assertion

ui/src/shared/components/PageHeader.tsx

@@ -48,7 +48,7 @@ class PageHeader extends Component<Props> {
     const {titleText, titleComponents} = this.props
 
     if (!titleText && !titleComponents) {
-      console.error(
+      throw new Error(
         'PageHeader requires either titleText or titleComponents prop'
       )
     }

ui/test/shared/components/PageHeader.test.tsx

@@ -0,0 +1,12 @@
+import React from 'react'
+import {shallow} from 'enzyme'
+
+import PageHeader from 'src/shared/components/PageHeader'
+
+describe('PageHeader', () => {
+  it('should throw an error if neither titleText nor titleComponents is supplied', () => {
+    expect(() => shallow(<PageHeader />)).toThrow(
+      'PageHeader requires either titleText or titleComponents prop'
+    )
+  })
+})