Convert old tests to use "react-testing-library"

app/soapbox/components/__tests__/column_back_button.test.js

@@ -0,0 +1,12 @@
+import React from 'react';
+
+import { render, screen } from '../../jest/test-helpers';
+import ColumnBackButton from '../column_back_button';
+
+describe('<ColumnBackButton />', () => {
+  it('renders correctly', () => {
+    render(<ColumnBackButton />);
+
+    expect(screen.getByRole('button')).toHaveTextContent('Back');
+  });
+});