add unit test

src/__tests__/header-test.tsx

@@ -0,0 +1,42 @@
+import * as React from 'react';
+import {Header} from '../header';
+import {makeTheme} from './test-utils';
+import {render, screen} from '@testing-library/react';
+import ThemeContextProvider from '../theme-context-provider';
+
+const pretitleFirst = 'HeadlinePretitleTitleDescription';
+const titleFirst = 'HeadlineTitlePretitleDescription';
+
+test.each`
+    pretitleAs   | titleAs      | expectedOrder
+    ${undefined} | ${undefined} | ${titleFirst}
+    ${undefined} | ${'span'}    | ${titleFirst}
+    ${undefined} | ${'h1'}      | ${titleFirst}
+    ${'span'}    | ${undefined} | ${titleFirst}
+    ${'h3'}      | ${undefined} | ${titleFirst}
+    ${'h3'}      | ${'h1'}      | ${titleFirst}
+    ${'span'}    | ${'h1'}      | ${titleFirst}
+    ${'h1'}      | ${undefined} | ${pretitleFirst}
+    ${'h1'}      | ${'h3'}      | ${pretitleFirst}
+    ${'h1'}      | ${'span'}    | ${pretitleFirst}
+`(
+    'Header has correct reading order with pretitleAs={$pretitleAs} and titleAs={$titleAs}',
+    async ({pretitleAs, titleAs, expectedOrder}) => {
+        render(
+            <ThemeContextProvider theme={makeTheme()}>
+                <Header
+                    headline="Headline"
+                    pretitle="Pretitle"
+                    title="Title"
+                    description="Description"
+                    titleAs={titleAs}
+                    pretitleAs={pretitleAs}
+                    dataAttributes={{testid: 'header'}}
+                />
+            </ThemeContextProvider>
+        );
+
+        const header = await screen.findByTestId('header');
+        expect(header.textContent).toEqual(expectedOrder);
+    }
+);